Thermostat controls in one room, temp sensor in another
 

I have a theater and would like to be able to adjust the temperature of the room without going into the room and possibly disturbing what's going on inside. Ideally I would like to have a simple thermostat control just outside the door with a wired temperature sensor located inside the room. I have found thermostats that will do this but they are a lot of $$ and have way more functionality than I need. Simple and inexpensive are the ideal.
Any suggestions?

You might be able to find a schematic and/or a kit for this on those hobby electronics websites. The Electro-tech forum comes to mind.

$20 in parts and a weekend to assemble/debug/test. The sensor IC itself is probably 50 cents.