Not brewing (yet; I'd like to get into it) but live in a really LCOL area and buy our kegs at the "Class Six" on the military base, so no tax, and the prices are pretty darn low there overall. I don't know what the store's cost is from their distributor. We usually pay around $140-150 for a half barrel keg.
As for the dollar beers.... are you talking 15.5 gallon (half barrel) kegs, or smaller (pony, 1/4 or 1/6 barrel kegs)? 15.5 gallon is almost 2000 floz, which gets you well north of 100 twelve-oz pours ASSUMING you have adjusted the line length and pressurization so that you don't get a lot of foam waste. (it would be 165 pours IF you could get them perfect, with no waste or pour-off... this is not typically realistic). Also, letting cold air into the "tower" helps keep the line and faucet cool so you don't have to pour off as much warm beer. I removed a baffle in the top of the kegerator so it now allows cold air into there.
But it's been a while since we bought one, so I may want to run an experiment on the next keg to verify my numbers.
Pony kegs are not worth it, IMO. They end up costing only a little less than the half barrel keg, but you get a lot less beer out of it, and I have found it more difficult to tweak the pressurization just right.
Flavor wise, some IPAs do better than others it seems. I don't drink them nearly as much as my wife but she doesn't really complain when the keg has gotten old. I find that keeping the lines clean (and not letting the spout dip into the beer glass during pouring - lets bacteria get in) makes a big difference in the flavor.
One thing I haven't priced out is the cost of running the additional mini refrigerator. I expect it's not that much, because it rarely/never gets opened, and holds a large cold mass inside.
Overall though, one of the biggest benefits I find with the kegerator is the reduced hassle and bottle/paper waste.