Here goes:
Maintenance records will go a LONG way. My '00 R/T has been great with very minor problems. I had to replace a power steering line and I had a Hughes plenum installed which ran me total about $300. I had the labour covered for the Hughes plenum installation with an aftermarket warranty; I just purchased parts.
Be sure to check the gas cap out as well. If it says "premium fuel" you'll have to fork out a couple hundred dollars more every year in fuel costs, so it's an option to consider. If it is premium fuel only, make sure you question the owner about this as it can damage the engine unless you baby it ALL THE TIME running 87 octane instead of the 91 as recommended. I'd ask them straight out what fuel they've been running in it, then check out the fuel cap. If you can manage a test drive by yourself, find an open road and put the pedal down, if you hear any ticking (ping/engine knock), stay away. If there isn't any and the vehicle feels tight and smooth I'd take it.
If maintenance records cannot be had, be sure to ask when the last services were performed, such as transmission, transfer case, differentials & even power steering fluid. If they are unsure, I'd be wary as they might not have ever been done. At least that's what I would assume, which can help you negotiate a much lower price.
Be sure to try everything out in the cab, right down to the horn, parking brake, and side mirrors. Depending on your area, a simple electrical gremlin can stop you from passing a safety inspection and set you back hundreds of dollars to get it fixed.
As far as maintenance goes, if you have basic tools and consider yourself to be relatively 'handy' you can do quite a bit of the regular maintenance. Things I've gone through have been brake pads & rotors, rear drum shoes, fluid changes and one set of tires. I put the operating cost around 29 cents a mile running 91 octane fuel and including related wear, such as tires, fluid changes, etc, all factored in (mods aren't factored in). I'm nearing 100K and have no transmission problems to report. I also tow frequently during the summer months and change the fluid religiously every 25K or 40,000kms. To put the cost/mile into perspective; a Honda Fit (as example only) will cost around 12 cents a mile providing you pay cash for the vehicle.
You can also visit http:\\autos.msn.com
www.edmunds.com and several others to get personal vehicle reviews. Something else to keep in mind while reading reviews: Someone who claims that their transmission blew at 90K probably never had it serviced, and didn't take it to the dealer for anything, just drove it until it died, and neglectful owners will write a review stating that the vehicle is horribly unreliable. If you put the time into it, it'll take care of you.