How about one of these. Not the sexiest car around but cheap and unreal mpg. Also has added bonus that you can sleep in it at race meets because the seats fold away completely.
Has the added benefit of being seemingly completely invisible to the law...
But as I said it is damn unsexy
There is one on ebay at the minute.
http://cgi.ebay.co.uk/1997-SUZUKI-WA...d=p3286.c0.m14