[Perfectlap]

Simple, try to find a car that still is under the 4 year powertrain warranty and then get an extended service contract. I bought a 2000 S for 30K a little more than I wanted to spend on my Boxster but my #1 motivation was low mileage. My S had a mere 10,000 miles at purchase back in November so I wasn't too afraid to buy an out of warranty Porsche. ALso, here in New Jersey used car dealers are mandated to offer a 90 day warranty. (mine is almost up).
It will take some searching but there are definitely deals to be had.
Do some searching for "problem" on forums like this one and the Renntech forum. And do some seraching for extended service contracts. Be familiar with teh Boxster tooth aches and you'll know what to look for when you check it out.
But one thing is for sure in terms of Maitenance, there will never be another car as easy as the Miata.