My 2005 AWD Astro van had 180,000 miles on it when I bought it. It had a few problems but all the major pieces worked and worked well. It left no oil on the street, it had no knocks or rattling, the transmission shifted well and didn't make any noises, it had good power and ran well, the rubber boots on the front CV joints were in good shape, and equally important the brakes worked well and made no noises. What it did have were things like the service engine light on, the A/C didn't work, the radio antenna was broken off, the heater/A/C blower didn't work, and the tires were shot. I am a mechanic so I knew I could take care of the problems. If I had to pay shop rates I'm sure it would have cost me $1000-$1500 to get it on the road.
By learning to service your vehicle yourself significant savings can be achieved. I bought an OBDII code reader off eBay for $25, anyone trying to operate on a shoestring should have one (assuming their vehicle has the OBDII diagnostic port), if for no other reason than it puts you on equal footing with the repair shop.
My OBDII code reader said the MAF (Mass Air Flow) sensor was bad and the engine was not reaching operating temperature, those were the cause of the service engine light. A quick search on the Internet revealed that the first thing to do with the MAF sensor was just spray a cleaner on it. $7 dollars later I was no longer getting that error code. The only way an engine does not reach operating temperature is if someone has removed the thermostat, put in one of too low a temperature, or it's stuck open, mine was stuck open. I replaced it and the associated error code disappeared. Now the service engine light was off.
The tires were the most expensive part but I found a brand new set that someone was selling on Craigslist. They had been pulled off a new Jeep that was getting a set of big, off-road wheels and tires. I got the four new tires for $250 and had them mounted for another $32. From Goodyear they would have cost me $600-$700.
When I looked at the van before buying it, I switched the A/C on and saw that the compressor was turning, so I touched the A/C lines around the evaporator and found that the lines were cold, freezing in fact, that told me that the A/C was working, just the blower motor or ducting was defective. As it turned out it was both of those, a plastic vacuum line (used to open and close the A/C and heating ducts) had deteriorated. I replaced the vacuum line and then found the blower motor resistor and connector burned, I had to replace both, and then I found the blower motor itself was shot. After all that the A/C worked like a champ. Trouble shooting this required being able to read the wiring diagrams and using a voltmeter, methodically go through the circuit, testing it until finding the defective component(s). It's not that difficult to do.
I guess what I'm really trying to say is that when buying an older vehicle it is better if you can work on it yourself. Things do fail as the vehicle ages, some of them are easy, simple fixes, but will cost you if you have to take it to a shop. Some of the fixes might be more difficult, but if you can do it yourself you will still save a bundle over the shop.