Not making sense to me, sorry...running a thermostat for TWO cages of DIFFERENT sizes? The larger will be too cool or the small one overheated, ya?

And "cheaper" doesn't cut it, IMO. Do it right! I don't recommend heating with bulbs to begin with...they are supplemental, yes, but heat rises & they're outside the
cage (MUST be for safety!) so most of the heat doesn't help the snake one bit, therefore you waste money. And should your "cheap" option to regulate such heat fail,
you can COOK your snakes this way. The only "bulbs" I use are on dimmers & supplemental* warmth only, esp. for snakes that like to climb & bask. (*not heating
entire cage with them)

UTH: heat rises INTO the cage, where the snake NEEDS the belly heat to digest, as opposed to bulb heat that's rising up up & away from the cage. And in case you
don't know, UTH like Flexwatt are very low wattage...cheaper to run. (but for the heat to remain IN the cage, you may need to insulate your cage, sides & back.)

Many keepers need both kinds (or other options like RHP) depends on how cool your house is (either in winter or using A/C), the kind of cages, & the kind of snakes.