I just equipped the last room with radio controller thermostatic valvas (from ELV), but now I have the problem that the kids don't close the door (if you have kids this should sound familiar

I have a RFXCOM, and the Homeasy/Chacon/etc. door contact sensors are not recommended (although cheap). RFXCOM recommends the DS90, but that is a whopping 50 euro per device. Quite expensive compared to the radiotor valve (only 30 euro).
Any suggestions for open door detection at a reasonable price ? RFXCOM compatibility would be nice, but I also have UTP cabling in most rooms. Basic requirement is that the signal should somehow get to my central server in the basement.
Thanks,
Soitjes.