Aha. I have noticed that the nRF24L01+ IC is very popular and pretty cheap, but it is not a single chip solution. I suppose I would combine this with an ATtiny or a really small ATmega328 and have my single-board wireless sensor node?
Either that or use the 8051 CPU that I have no experience with in the single-chip nRF24LE1, which I found on their website.
I am mainly looking for someone who has done this with this pricing in mind before. It seems that everything I read about Arduino sensor networks involves the Xbee + Fio or some variant.