There are some reasonable looking sub 500 cars out there.
Problem is it might be knackered and if you dont find out till after you have bought for £500 you are pretty much stuck as I dont think dealers will waranty anything under a grand. Be suspicious of, recently changed oil & coolant ( may be hiding a blown headgasket esp on old cars ) - no paperwork to back up milage such as service book - as well as the obvious knocks, evidence of crash damage etc.
Anyhows not in your area but here are some examples of whats out there...
2.5 V6 vectra & a SAAB both with around 70k
on the economic on petrol side ( and cheap if something breaks)-
Swift GLS with 35k a 1.1 pug 106 with around the same and an Old shape Fiesta - not a looker now but a future classic with 42k on the clock you will be able to sell it for what you paid for it probably!