Have a look on
www.wscc.co.uk. Plenty of help and support there and you can find your local meet and look at the cars in the flesh.
Westfield are also quite happy to give test drives. Just give them a call and they'll let you pop over drive one of their demonstrators
sideways to see if you like it. It's a one way street though. You will be hooked once you've driven one.
I think you generally get what you pay for with kits. Go and buy a Caterham kit and you'll get every last nut and bolt, spend a couple of weeks bolting it together and you've got a finished car. It'll cost you, though.

The Westfield kit is pretty good. More work to do, and you have the option of building from a donor car instead so there'll be some reconditioning of parts required if you take that route. A modular build will give you everything you need and an easy way to spread the cost as you build up the modules.
The Dax Rush I'd place at a similar level to the Westfield, possibly a little more work required. :-/
I don't have much experience of other makes but get hold of a build manual and see what's involved before you commit.
Kevin