If you have RTC (real-time clock) available at each node (for "precision" timing), what about the HopeRF transceivers? They are smaller, lower-cost and probably lower power than the Xbee "expensive spread".
How low-power do you need?
Looking a ANT, specifically the ANT3, "The AT3 family products is so-far the lowest power consumption solution of ANT." This uses nordic nRF24L01(+) and pairs it with an MCU. You already have an MCU. Why not just use the nRF24L01 directly?
When will Mosquino be ready? Is it possible to pre.order it?
For ANT specifically, the price difference between the AP2 chips (nRF + 8051 core + stack) and naked nRF24L01+ is about $1.50 (qty:1); for that price I'm OK with letting someone else have that headache ;-)