Heating multiple scorpion tanks cheaply.

How do you guys heat multiple scorpion tanks? My room's currently at 21c during the winter and jumps to 25+ during the summer. I'm curious as to what I should do to heat up more than a few tanks at once. I have a few Asians forests (Pandinus cavimanus, P. imperator, Heterometrus cf. petersii) that are fine at those temps, but I'm looking to pick up some desert scorpions soon. I was thinking on a Hadrurus sp. and a Hadogenes sp.. Any help would be appreciated!

If the species tolerate the same conditions then one larger enclosure with partitions. This enables one volume of air to be heated. I have a 3' aquarium with three glass partitions about 8" high. In each corner I have a 8x8"smaller aquarium. I keep 5 P. Trans like this

I use a cabinet / vivarium conversion with shelves, have the lower temp specimens in the bottom shelves and deserts can sit under lower wattage lighting / near a temperature controlled ceramic towards the top, allowing for cooler species at the bottom such as Euroscorpius and Hets, and then deserts in the top. Many different ways of doing it though.