This is the best off the shelf diy stirling alpha engine start we have come up with so far.
This Stirling Engine has shown signs of successful operation. It also works excellent as a Steam Engine. I have another compressor that I am converting into a DC motor:-)
These compressors cost about $100 on EBAY. Make sure you buy the compressor pump at a 90 degree angle.
This based on the Alpha Stirling Design that you can find here: