A 3-d background inside the tank gives more usable space for the frogs (and looks nicer

).
You don't seem to be in a hurry here, that's a big, big plus for the budget conscious. You can save on many things, make your own ABG, collect your own leaf litter, keep your eyes open for smaller discount plants from box stores, propagate and grow them yourself, etc. A carefully detailed plan from the outset will help you know what deals you should be on the lookout for.
It might not hurt to try a smaller build first. 20 or 30 gallon used fish tanks can be had for a song if you patiently watch kiji/craigslist/garage sales. Trying a few things out on a smaller scale can help you plan for the larger version and save in the long run.
Good luck!
