Ok sounds like your house is pretty cool. You may struggle maintaining high enough temps. The biggest pros about CHE would be that they heat a large amount of space, are fairly inexpensive, and can be run 24/7. The only con is that they can dry out an enclosure unless you take measures to maintain humidity. I'd definitely recommend covering the majority of the screen with plastic wrap/aluminum foil/duct tape.
The issue with UTH is that they're small. If you only get one for the hot side, the cool side will be sitting around 70, which is far too cool. You could get away with a CHE on the hot side and a UTH on the cool side. But UTH are pretty expensive for what you're getting. I think even the medium size runs about 25 bucks. Flex watt can be a bit confusing, but there are awesome tutorials on how to get it set up, and it's only a few dollars a foot.
Oh, and I forgot to add, you'll need a separate thermostat for EACH UTH, which will really dig into your budget. Unless you get something like a herpstat 4.