I don't remember who said it but I have to say it is not always cheaper to heat individual enclosures. If you're talking just a few cages then maybe but if you have a lot of enclosures it's best to get them all in one little room then heat the room to the ideal background temperature, get enough bulbs and UTHs going in a small room and you'll find it will heat up into the high 70s anyway.
I keep nearly all my snakes this way (some have spilled out into the rest of the house so they get individual heat) with the boids getting additional heat at a basking spot which I provide with either a UTH or an overhead bulb.
On what Ken said though, I know some folks that do things the exact same way. I would be curious though what kind of success people have had breeding boids in particular without a heat gradient. I haven't looked at this topic enough to even guess what the answer to that is, I'd be interested if anyone has had any luck doing this. It seems successful reproduction is the best indicator we have for proper husbandry, besides healthy growth and just plain not dying.
I feel a little light headed... maybe you should drive...