If you are racing on the cheap, The RX-7 is the one of the best platforms for building a really fast car.
The Z-06, the SVT, are also great choices. Though the 'Stang is kinda heavy.
The Supra is only truly awesome if you don't go too wild with mods. Over about 700 Hp you have a barely tameable beast that does little more than roast its rear tires.
One of my favorites is also the Lancer EVO6 or EVO7.
Both are available for under 26,000cr. And can be built into really fast, easy to drive cars.