I have the exact same problem as you do and here is how I fixed it:
I have all of my snakes (3) in a 4-shelf rack organized like so
Shelf 1: Heat Cable
Shelf 2: Ball Python
Shelf 3: Florida Kingsnake
Shelf 4: Cornsnake
Now, in order to keep ambient temps up in the ball pythons enclosure (its usually around 68-70 in my room if not lower) I ran the heat cable along the bottom of shelf 1 and completely covered it with duct tape. I then taped the front entrance of shelf 1 completely shut with duct tape so it will retain heat. Now, after about an hour of the heat cable warming up (on a dimmer mind you) the heat soaks through the wood and radiates down into the tub without sucking out the humidity. Voila! Instant climate control (Esp. with a good thermostat such as the Herpstat PRO)! Only affects Shelf 2 also.
Total cost:
Rack (If you don't have one): $250-300
Dimmer $10
Heat Cable: $16
Total: $276-326 before tax
Now, if kept in a tank my suggestions would be to buy a very cheap melamine shelving unit/drawers from target (20-30 bucks) find a tub that fits, put her in it and then run the heat cable along the top while making sure to cover the cable so no heat escapes. Or you could run the cable through the actual shelving unit and have it radiate inside of it.
So now pricing is:
Dimmer: $10
Heat Cable: $16
Shelving (make shift rack): $20-30
Total $46-56 before tax
Now, if neither of the above is an option, you have a couple of other options to heat the tank.
Option 1: Buy a very small electric heater and place it close (not to close!) to the tank. Monitor surface temps to make sure they aren't hitting 100+ (I've seen those heaters put out heat thats 200+) and don't leave on any long trips.
Heater: $20
Thermometer (Probe for glass): $12
Total: $32 before tax
Option 2: Buy 2 CHE (you may be able to get away with 1 but I'm not so sure because of the low temps in your room), place on either end of tank, fiddle with em till you hit your desired temps, monitor temps frequently, wrap the outer tank in some kind of insulating material such as pegboard, etc and cover half of the screen top with foil, wood, pegboard (Basically an insulating material). Monitor temps as much as possible to watch for possible overheating.
CHE: $60 (1 is $30)
Dimmers: $20 (2 required)
Tempgun: $25 (RBI 205 I think it's called. Its on reptilebasics.com) Not required but recommended when aiming for ambient heat with CHE
Pegboard: $5-15 depending on location and store
Wood/Foil: $5-10 depending on which used/location/store
Total: Best Case (no tempgun): $50
Worst Case (No tempgun): $105
Ideal/Worst Case (includes tempgun): $130
Hope you get some ideas from this! Good Luck!
-Andrew