Calling for quotes and from the few who answered its a $850-$950 job. Requiring 6 hours of labor and an AC recharge. This seems insane for something that's bound to happen over the life of a car when you're using a steel bolt on aluminum threads!
Sounds reasonable enough for a shop. It's a FWD car, so at a minimum, you're likely to need to disconnect most of the wiring and plumbing from the engine (which is where the AC recharge comes in - the AC compressor is on the engine, with lines going to the car, though you might be able to avoid it by removing the compressor), pull the engine from the transmission, and either find an opening to work on it (possible but unlikely), or pull the whole engine.
Oil pans on FWD cars are a non-trivial thing to replace.
And... no offense, but it's not "bound to happen." I've never seen a stripped drain plug. I've owned a lot of vehicles with 200k+ miles on the odometer. Leaking oil pans, yes - but from failed gaskets around the drain pan to car, not from the drain plug.
I also regularly change my own oil, install quick drain plugs on vehicles where it makes sense (so I'm never having to remove the plug after that), and I use a wrench to tighten the plug to something resembling torque spec.
It's not uncommon to need to use a jack to pop the drain plug free on a new car, if the previous owner has had a habit of using shops for oil changes. Every damned quick lube place out there puts about 5-10x the torque on the drain plug it needs. If they bother to reinstall the thing at all.
So we haven't done timing belt, pumps or any of that major stuff that I assume may be coming as its at 105k miles.
Your car is not worth what you think it is. You'll either need to find a sucker, or lower your asking price significantly, if you want to sell it.
Could the oversized plug been installed incorrectly originally, thus leading to the quick failure?
It's an ugly hack of a solution for a problem that shouldn't happen, so... who knows. There's a normal seating area for the drain plug, and an oversized plug involves drilling and tapping that. Did it stay in the drain plug area or expand into the thinner oil pan metal? No idea!
Should the oversized plug have failed so quickly at so little miles or is that not really a factor?
It depends on how well it was done. You said Midas did it, so I'm going to guess it was poorly done by someone who may or may not have ever done that before.
Do they make an oversized plug that would be reliable in the already enlarged hole?
Depends on why it's leaking. It could just be loose. It could be that it needs a new copper crush washer (which should be replaced every oil change, and realistically needs to be replaced every few or you're going to have leaking issues). It could have cracked the pan if it was poorly done and stressed. Without more details, it's impossible to say.
Would I have any chance selling it for a reasonable price on craigslist with it leaking the way it is? Say a mechanic who can spot easy money?
No. Based on your reported maintenance history of "Ignore it, it's probably fine," anyone halfway competent should be able to tell it's a rolling pile of shit that's been neglected, and run for the hills. You might be able to find a sucker, though.
Longer term... If I fix it with another oversize plug should we just sell right away? Should we keep it around in case we need it later knowing we've had the vehicle since new? Would you change your answer if we spent the full amount and got the oil pan replaced?
If you get it to stop leaking, you can probably lower your asking price a bit, sell it, and make it someone else's problem. If it were just the drain plug, I'd say a new oil pan would fix it, but the other maintenance history you report says it's likely to be a problem in the future.
Yeah I doubt they installed the oversized plug properly with a cleared hole and rethread. The only charges were for the drain plug and no labor.
It should take some labor to do it properly... so I have no idea what they even did. If it was "Find a bigger plug laying around and jam it in," I'm not surprised it's leaking. May very well have cracked the pan over time.
So maybe I'll investigate if a real mechanic can do it properly and see if it holds before going through drastic measures. I'm not sure what else is nearing failure on the car other than new brakes (they said rotors too but I'm skeptical) and AC recharge.
Why are you skeptical about the rotors? 100k miles is reasonable enough to need rotors. Are you skeptical because you've actually gone in there and measured the rotors, or because you just think the shop is out to try and get more money from you? I know you haven't gone in with a set of calipers to measure the rotors and compare them to the wear limit, though.
Seriously, I'm sure he's probably gone 10k between oil changes before and he once drove to work with the car in the red heat zone and thought it was fine to drive home too (maybe we should sell hah!).
So... low coolant? Failed radiator fan? No idea and it just went away? Sustained overheating on modern engines often causes head gasket issues (those, too, are expensive to replace). A modern car should not overheat unless something is significantly wrong - they're tested in insane thermal extremes during development, so you should be able to run a car at 130-140F, in the sun, with the air conditioner blasted, without overheating. Pressurized coolant systems are one hell of a drug. :)
We get into an argument if I even mention we should attempt to fix anything ourselves on the car as it would "waste our entire weekend" regardless of how much money it would save. So if I were to mention doing oil changes ourselves yeah not gonna happen. Its easier to just print out a coupon to the dealer and tell him to go there and say no to anything they recommend.
I don't mind "wasting a weekend" to save a few grand. :) I do my own oil changes, obviously, but I also do a lot of my own work, because I can, and it's cheaper. YouTube makes it easy to learn how to do pretty much anything on any reasonably common car (which yours is). It's a lot more interesting when you've got a car that was imported for just a few years, has no user community, and you can't even get half the parts. That's not a problem for you.
But, seriously, even a few hours on a weekend to do an oil change for the first time with YouTube will teach you a lot.
Sorry for the rant. I just hate dealing with car crap. Everything to do with cars just makes me feel like I'm getting ripped off and inadequate that I can't/won't take the chance on learning and fixing it myself.
A basic set of wrenches is sufficient to change oil. You might need an oil filter wrench if it's particularly tight. And a drain pan. Start there and go!
DH can be absolutely zero help sometimes unless I put my foot down and keep pushing him to do it. On a positive note, he did willingly learn to replace the headlights on the other car which go out all the time.
... why are the headlights going out all the time? That's not a thing that should happen more than once every few years.
Maintenance or upkeep of anything (not just cars) is not my husband's strong suit. Neither is foresight about how minor things can cause bigger problems if you consistently do something wrong. And that is a major reason why we do not own a house because I would be overwhelmed with having to look out for and do everything. He's great for other things, like not being overly analytical and critical like me. He can actually make a decision and go with it which is what I need!
If he refuses to maintain a car, and doesn't understand that minor problems need fixing before they cause major problems (if that drain plug failed on a long drive and you didn't notice it, would he have stopped driving at the oil light, or waited until the engine sized?), and you aren't willing to do it, might I suggest a new car lease? It's financially painful, but you'll have a vehicle you can safely ignore for three years or so.