Went to edit my post but apparently 10min has gone by, so I'll add this:
Glass tanks are definitely harder to maintain as you've noticed. I had luck tinfoiling the top of mine, and insulating the sides with some cheap "school project" black foam board from the hobby shop near me. My house is usually around 68-70F, and I was able to maintain 80 ambient with just a single 75W ceramic heat emitter, providing a hotspot of 90 with an ultratherm or equivalent under-tank heater. The CHE was pretty much at 100% all the time due to my home temps, but the UTH floated around 20-30% to keep the hotspot warm.
Main problem I had with the glass (exo-terra) was humidity. It was a constant struggle keeping the tank misted especially during a shed cycle. Eventually that led me to the PVC cage, and I have to say I couldn't be happier now. A single pro-heat RHP keeps her hot spot at 90 and 78-80 ambient/cool side easily and I never have to worry about humidity again, it's always 70% or higher.
Maybe you can try something like the foamboard out to keep things easy and cheap for now, and save up for the nicer setup in the long run
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