The piggy back system I suggest you look into is the MAF Translator PRO.
Having said that, the basic unit will cost $400.00, with the complete system (Translator Pro, GM 3 bar MAP sensor, GM air temp sensor, 9' speed density harness, wide band sensor / harness, and boost control solenoid / harness) around $750.00.
www.fullthrottlespeed.com is a good site to go for information and sales.
WWW.horsepowerfreaks.com and
www.suprasport.com sell the unit as well.