What I'm using right now is just a work light reflector with a single spiral bulb (as suggested by a couple of people on this forum) and for 8x10 images it's taking around 18 minutes to expose a Vandyke. This is with a 27W bulb. Total cost $25ish.
I'm considering making a 2x3 grid of the same bulbs and wiring it into a plywood box (I do a lot of electrical work so I'm comfortable doing this and have most of the stuff already) - so that would pull 162W and hopefully the exposures would drop down to 3-5 minutes depending on what distance they end up being from the paper and so forth.
I'm not experienced enough to know what exposure times for different processes are, but I can't see a setup like that having a major effect on your power bill even if you make quite a few exposures with longer run times.
I was thinking I'd spend around $150 on it but again I have some of the stuff.