hi Nick
yer cars do come up forsale ever now and then. My brother had a car he sold a few months back. You would expect to pay from around $15,000 up for a race car zed (prob 20 up for a fast one!)
It definatly works out cheaper to buy one than build one as my brothers cost him about 15,000 to build (not including labour) and I originally brought mine for 16,000 and mine was a much quicker car (better bits like lsd, better g,box better engine etc)
If I here of any decent cars up for sale I will let you know.
Ash