I've had good luck with the nRF24L01 modules. You can get them for less than $4 each on ebay. Here is a url with some guidance: http://www.atmega128.org/#nRF24L01. They have good range, low power usage, 100 software selectable channels and can be used as transmitters or receivers.
Please enter a valid email to subscribe
We need to confirm your email address.
To complete the subscription, please click the link in the
email we just sent you.
Thank you for subscribing!
via Egeo 16