The Cypress WirelessUSB solution is very cost effective. We’ve used it before for an 8:1 system (8 keypads to 1 dongle) and it’s only a couple of bucks per unit for the wireless hardware if you do your own PCB.
Module-wise, Arteflex is one possible source.
http://www.artaflexmodules.com/
The dude that makes the MetaGeek WiSpy is using a WirelessUSB dongle from Unigen.
http://www.unigen.com/product_list.php?cid=16
You might also consider Nordic RF modules or www.Jaalaa.com
