Missed this thread the first time around...
The biggest difference is opportunity cost (assuming positive returns on investing money saved) which most people don't factor in.
This is most certainly true, but the opportunity costs of people's time is also highly relevant. Those tradeoffs are what makes this math so complicated (and to a degree, emotional). It's really neat to see the different data points.
I'm going to add my info since I purchased new and I do almost no work myself on my car... So I think this is also an interesting anecdote to see (if one that folks around here scorn). Since there are a few different things going on here (new vs used, calculate total cost, cost/mile), I'm going to break it out a bit so folks can see different numbers.
There are a couple of instances in this thread where people have counted the entire purchase price as a cost, but are not entering the car’s current value as a credit offsetting that cost.
My car was totaled in the week this thread was originally active, so I have a very clear value to close that loop :D
$29,142 - Purchase (new/Aug 2006)
$3,229 - Maintenance (dealer through 65K miles, total up to ~115K miles, only non-base/scheduled maintenance is new rotors/brakes [a second set after what is shown below])
$2,298 - Tires (3 sets: winter + 2 all-season)
$165 - New Brakes/Grind rotors (partially subsidized by manufacturer due to wrong brakes installed on original vehicle) (2008)
$216 - Cracked fog light (2008)
$370 - Broken rim + new pair of tires (2018)
$0 - rims for winter tires: Bought in 2007, sold in 2015, $500-$500= $0.
-$6,400 - Totaled May 2019 (payment from insurance)
$5,000 - Estimated Collision/Comprehensive Insurance (dropped in 2014) [I can't pull up the early years due to change of insurance company when I moved]
$34,020 over 153 months of operation = $222/month or 29.6c/mi
Note #1: Add "any car will need this" fuel [~$10K], liability insurance [~$7K], and registration [~$1K] to get to $340/month or 45.2c/mi
Note #2: The only self-work was the fog light, because the installation cost is silly (then again, so is the part cost at $216)... everything else was done by a dealer/shop.
Note #3: Free new brakes at almost 25K miles due to manufacturer mistake probably was about ~$250 cost avoidance.