Hmmm. Let's see. your typical air ride needs the following parts:
Air springs- $65-75 each and you need 4.
Air tank- 5 gallons about $50
Compressor- Few hundred depending on what type you get.
Valves- $35-60 a piece, 2 for each spring
Airline- pretty inexpensive
Misc wiring and other stuff- $$$
All in all, it's going to be pretty expensive. I plan on doing a full air-ride, but only because it's awesome.