Go to www.westfield-sportscars.com.au
and check out the cars there, ive been in the green car before, and it is awesome!, that has a naturally aspirated japanese engine (i forget what exactly), a recently built car has a turbocharged S14 silvia engine fitted, and that looks to be a ripper. I've been told that the complete chassis retails for about $10,000, and it weighs about 600kg when completed, depending on the driveline choice.
Also, the owners of westfield sports cars also own Replica Motor Company, which make a cobra kit cars, one of which i was a passenger in on the same day as the westfield, and i liked them both very much. i'd recommend one of these cars