Why not buy the micro controller and simply swap the micro controller into the arduino?
You don't need to buy a new arduino for every project.
http://www.instructables.com/id/The-...Teach-You-in-/
As for programming:
http://hackaday.com/2010/10/25/avr-p...-the-hardware/
I'm working on building a MPGunio clone that ditches everything unneeded to give fuel consumption readout, target cost is $10 and an hour to assemble and install.