Dont get a pre programed one from Ebay mate...since when did Ebay stuff became trust worthy...IMHO i dont think $500 to get it flashed isnt expensive...its the most vital part of your car and your longevity of your motor mate...so really your call...
I have heard off Jeff at Turbo tune doing these and apparently they are really good tunes etc...give him a call and find out mate....i also dont think he charges $500