I use XRF modules £9 each over a mile range.. plug and go. http://www.ciseco.co.uk/content/?p=1738
They sell them on ebay for 1-2 off you'll pay £11.88 **broken link removed**
Cheap and easy are mutually exclusive. You can get super easy ones that are expensive or hard ones that are cheap. I think you need to define what you think is cheap and how easy you want.
I think the RFM12B's are good as well. If you want to be able to talk both ways then they are the same price as dual transmitters and dual receivers for the link style modules.
If you want super easy then the XBee stuff is for you.