The Engine computer was changed in 2003 to a Next Generation Controller. I haven't seen much in the way of parts or ECUs after 2003. You may have a difficult time finding much of anything since the Neon have gone away.
In 2003 the compression was reduced to 9.3:1 which is good for mild turbo charging. If you have $5000 to spend you could have a turbo put on it without having to rebuild the engine. You can safely get 6-8psi boost with good tuning and an intercooler.