I live in SD so same weather here, now my house is climate controlled, during power outages the temps in our hose hit the low 90s. All my cages are either PVC or in the case of my tegu a heavily insulated wood cage. They seem to hold stable temp pretty well. All that being said another snake option would be any of the antaresia species (ex childrens python). They are from Australia and like a nice warm environment with a hot basking spot.