We find that plexi glass does scratch up easy and is harder to clean than glass.
If you go to your local Speedy auto glass or somewhere to that effect they cut the glass for cheap and to the exact size you want.
The enclosures do sound great!
If you want to make some affordable go with other some of the cheaper styled knobs etc, you can get some awesome looking door handles at Home Depo of lizards for a lower cost than brass knobs. Instead of using solid oak also look into some of the softer woods like cedar and pine that are more affordable but look great as well.
Also make some that are just frames like Zhar mentioned that are a little more functional for smaller species untill somebody could afford something a little more luxurious!
From me Christina