Be VERY careful what you buy. Alot are absolute Shite (namely robin hoods!). Westfields are excellent with alot of choice with engines/ suspension etc and reasonably good value (compared to a caterham). There are cheaper ones which can be made into very good cars, just depends on the builder.
Just try to stick to common drivetrain parts unless you want loads of very late nights. My RX7 turbo powered westie is being a bastard to get finished, just hope its going to be worth it.