X10 is a good suggestion, but the quality may not up to par. IP cam may be another option, the quality is getting better and prices coming down. 20 meters is well below the cat 5/6 segment length limitation (10/100/1000base-T). Some of the IP cams are PoE, if you need that option. I would not use wireless for bandwidth reasons.
Quick and dirty: If you already have a cam you want to use, maybe get a $50 laptop and a 50 foot cat 6 cable ($15) from ebay, plug in the network cable, plug in the cam, you're done.
I'm sure there is a vid guy lurking around...maybe your post will flush him out into the open... :-D
*this prob should be moved to "Random Discussion", rather than stay in "Ask-a-Model"