lavalamp bulbs are 25W in the majority of lamps. If you used a 24/7 heat source and deposited most heat to the lava (rather than the sides of the metal base) it could be functional with 15-20W worth of mining power, possibly just some stick miners glued to the bottom part of the glass base
You can get a 100W Grande Lava Lamp for $100.
http://lavalamp.com/grande-lava-lampYou could probably get 250GH/s out of that much heat. Add a TOR router, a p2pool node, a controller, some LEDs, and you could ask $250 for it easily.