What about the Mote system? It has come a long way. Has it come far enough to be easy and cheap for what I want to do? Here is an overview page of the open source meshworks software dev platform. There is XML gateway middleware, mote firmware, etc.

Crossbow makes motes, gateways, etc. They make a very small module for embedding, but offer no pricing. The lab-scale motes are over $100 each. The hardware gateway is $450.