Get a MAF, air intake, and the section of harness that goes from the MAF to the main engine harness. I think I did my conversion for about $200-250. Most of the cost was my CAI.
MASS air conversion instructions from http://www.stangnet.com/tech/maf/massairconversion.html FREE
A9L (5 Speed) computer from junkyard $100-$150
A9P (Auto or in a pinch, 5 Speed) computer from junkyard $100-$150
70MM MAF from 94-95 Mustang GT - $40-$70
MASS Air wiring harness kit $30-$85
The whole thing is probably less than $300 using junkyard parts.
A9L computers are 5 speed only
A9P computers are automatic , but will work with a 5 speed.
If you want to save, do as they mentioned above and get the parts used.
For example, search in the classifieds section or PM me. I have stock throttle body, stock inlet tube (MAF to TB), stock MAF, and stock airbox, as well as a K&N air filter that drops in to the stock box.
Either way, buying it separately is the way to go!