You will find a few pieces cheap, then find some parts expensive/hard to come by - such as the throttle servo. You may end us spending a bunch of time only to save a few bucks at most.
You are better off trying to find someone selling a used complete system, but don't expect to find them giving that away either.
You can save a few bucks with this system:
http://www.hydrophase.com/
It didn't meet my needs but will likely meet yours.