Like has already been said, best setup for a wood cage is a RHP with a decent proportional thermostat. Yeah, I know, not exactly "Budget heating" but IS best and safest option. You're looking at a couple hundred to get both.
You can go less but each step away does add additional risk.
Other more risky options for the actual heat element are....
Ceramic Heat Emitter inside cage pointed down. HAVE to put a gaurd around it!!!!
Light bulb? Way back when that's how my original cage was heated but it was in a well insulated room with little temp variation.
Flexwatt recessed into floor.
Other options for Thermostat are:
Ranco on/off
Cheapo on/off
Dimmer switch (lousy choice in an area with larger temp fluctuations)
This is one point many simply do not get, a properly set up decent size enclosure can easily cost more than the occupant!!!
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Thanks,
Dave Colling

www.rainbows-r-us-reptiles.com
0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)
LOL, to many snakes to list, last count:
26.49 BRB
20.21 BCI
And those are only the breeders 
lots.lots.lots feeder mice and rats 

