BTW, when my house is at 70*, my corn snakes can mostly be found in the unheated areas of their cages, using the UTH only sporadically, like after feeding. The temperatures they seem to prefer closely approximate what we are comfortable with, about 70* or a little higher, with access to UTH when they see fit. So even if you go ahead with a PVC cage, make sure you aren't over-heating them. Corns are wonderful pets: docile, nice size, pretty, & for a 'bonus', among the easiest to keep. I've kept (& bred) gopher & bull snakes, I enjoy them too, but if you're short on space, a corn snake is the better choice between them.
You might also consider an Australian spotted python- they stay smaller than most corn snakes, and would probably do OK in a plastic cage, as they do need more warmth & humidity.I've only known the one I have, an unwanted rescue...she is "all python" (really feisty about food, easy to feed on f/t too) but docile to handle. Very alert & likes to bask on branches at night.