If you are still looking for ideas:
I have had a huge 40 gal tank since November. Despite all the suggestions to buy new heating equipment, use a tub instead etc etc, I found other ways to retain humidity that were much less costly than changing too much. My methods still are:
A couple of damp washcloths (you can move up to towels if you want),a layer of cut plexiglass that has an opening for the lights, and some dry regular towels on top of that if needed. Those are best for retaining heat.
Inside I use sphagnum moss, repti-bark (I find it hold humidity well without getting nasty, and unlike loose fiber won't get dusty when dry) mixed with an area of tropical mix (dirt-like) bedding on the cool side.
Most useful:
HUMID HIDE. Slapped one right in the middle and have the tropical bedding and a pile of moist moss in it. My BP spends a lot of time in it, and since I added it, he's had flawless sheds combined with occasional misting. It creates a little spot of higher humidity than the baseline 50 my tank is at often for when he needs it. You can make one out of a container that's a good size and save some money there too if you'd like!
I figured these out with trial and error here and there, and he turned out just fine without me wasting all my current supplies and getting all new.