The easy answer for those on a budget is always the Mazda MX-5 Miata. There are, however, a few alternatives... and one of them just happens to start with the MX-5 as platform to build upon.
Enter the Bauer Catfish
Enter the Bauer Catfish.
The team at Bauer have started with the already-out-there idea of shoving a V-8 engine into the diminutive body of the MX-5. This crew has taken that idea a step further, however.
A lot further, in fact. Rather than just rework the MX-5 to fit the needs of the engine, the Bauer Catfish takes what it needs from the Mazda and applies it to a tubular chassis. This is similar to what Factory Five is doing with its new 818 that kills an Impreza in the name of fun.
The Catfish gets some Mazda guts, shoves them into the lightweight chassis, and then adds in a LS motor courtesy of the General. The resulting car looks like the unholy love child of a MX-5, a TVR, and something from Aston Martin. We said it was unholy... but we mean that in the best way possible.
Should you desire something like this for your own garage, you'll need to cough up around $14,000 plus the cost to find a donor MX-5.
For a slick-looking track machine, that's actually quite a bargain.