I tested a rig with a peltier cooler a while ago. Total cost about 30-50 dollars, maybe? Peltier element through eBay from China (a 12706), two heat exchangers (these: http://www.ebay.com/itm/2-Pcs-Water-Coo ... 1340870314
) bolted together around the peltier unit, two small water pumps, some piping, an old computer PSU and two large plastic boxes from IKEA. Some drilling, bolting and connecting hoses later I had a system with a warm water side at about 35 degrees Celsius and a cool water side steady at 14 degrees Celsius. Both about 10 gallons worth. Ambient at the time was about 21 degrees Celsius. Yay for arduino and cheap temp sensors from China...
I stopped the test after one day, because my old computer PSU was a bit too long in the tooth and had developed an irritating whine. A lot louder than the two constantly on water pumps. I have since ordered smaller, hopefully more silent pumps and have some other PSU's waiting to be tested.
The idea will be to run the cool loop through the bottom of a (still to be built) HL terrarium. Possibly including a mister somewhere in the loop. And maybe the warm loop through another terrarium for LL conditions.