I don't have a frog that requires the use of ABG, so you might try to get some info from those that do. It may be that you don't need to cover all the bottom with ABG. The rest could be other features that are appropriate for your creature, or just something that adds interest.

I'd also try to get an idea how often you are going to have to replace the ABG. I've seen a few posts that seem to indicate that it might need replacement several times a year. So if the 100 bucks is pricey, it will only get worse. <<grin>>