what vehicle are you buying one for? if it is just for mileage, its probably more money than its worth, as most that are ready to go are in the 4 digit range and still require tuning.
I am going to go with megasquirt 2.0 to convert my 84 bronco to efi. I chose it cause its cheap, proven, simple and I can do it myself. it is also completely tuneable and has wide band o2 capabilities.