If you're really interested in the 'it's a jet ooh aah' factor and not the performance, you have two relatively cheap and practical solutions:
- keep a traditional engine, and mount a
JFS100 or similar APU or starter turbine on your decklid area. They won't produce much thrust, and they're only designed to be used in bursts, but you'll definitely have the cool factor and it can be self-contained. Prices are in the four figures for used/near service intervals.
- Get an RC gas turbine and hook it up to the exhaust side of a turbocharger that feeds your conventional engine, similar to
this. Prices range from 3k-6k for a decent one. look at jetcatusa or similar.
These fairly basic setups will require lots of planning and technical knowledge to make them work. Anything more ambitious would just be exponentially more demanding. Here's two sites to get you started on your research:
http://www.aardvark.co.nz/pjet/http://www.gas-turbines.com/