No mileage is "too high" per se, it depends on your expectations. What you're looking for is maintenance, maintenance and maintenance. I've seen 70K sheds I wouldn't give $500 for and I've seen 250K well-maintained vehicles I wouldn't hesitate buying for $2000.

All cars experience a bit of a "mid life crisis" around 150-200K mi, so you'ld want either a vehicle that has some miles to go, or a vehicle that's been through that and has had its problems properly fixed (as opposed to "live with it and hope to sell it to some sucker before it blows up"). If you're handy you could even pick up a car with a few problems and get your parts cheap at the pick'n'pull.

OK, now on to specifics.
Forget about turbos, diesels and 6-cylinder cars. If you're going for an automatic forget about the ZF box, AW are stronger. The 4 cylinder engines are pretty well developed, so few problems there. Again, regular maintenance is more important than mileage per se. 88 onwards has fewer electrical problems and better rust prevention. Interior trim and electrics gradually improved, but the smooth dash (91-onward) 740 and the 940 series are what you really want if that's a consideration for you. Avoid nivomats, they're expensive to fix if they break. Ditto for independent rear suspension. Tailgates are aluminum and Volvo didn't really get the painting process right until about '90, so there may be some bubbling. Make sure all electrics work as expected.

Bram