Ive seen them online for a few hundred dollars, I made my own, and for what we have in it (probably at least $200, and I got my glass for free!), I dont think Id pay that upfront to buy one. But mostly bc Im a big "i bet I could make that" type person. Im sure theres a profit somewhere to be made with these, or there wouldnt alrdy be companies out there that sell them. If I were you Id look around online and see what they go for, figure out how much it would cost you to make one, and see how much of a profit u could rlly make trying to sell them. Also factor in if your going to ship them and how much thats going to add on to them consumer, bc I bet shipping would be terribly high on one (I know mines super heavy) Plus many ppl buying beardies w/o much research 1st (like I did, and Im sure many many others) wont realize they need such a big viv, so you could probably make ones in a smaller size (than the 4x2x2) to to sell (which would also work for smaller reptiles). I know that seems dirty, and we hate when pet stores sell us tanks too small to last long, but I can honestly say if I woulda been told hey u need to have a 4x2x2 for it when it gets bigger, I woulda looked at my little 6 inch beardie and thought, okay they are crazy and are just trying to get me to spend more on a bigger tank (when in fact the opposite would be true)
Id also check and see if wherever u are has local reptile shows (here we have one every month) and you could think about making a few in different sizes and renting a table there to sell them. I think its a very good idea tho, especially for those who are less handy with building things and want a rlly nice viv (maybe build a few that are a little shorter and put mesh on part of the top for lights in case someone with a snake may be interested). If you can find suitable wood for cheap enough, and get a good deal on the glass, or plexiglass, lexan, whatever (cause I know those are the 2 most expensive items) then I def think it would be worth building 1 or 2 and giving it a go. If anything you must enjoy building things to want to do this, so youll have fun, and you can let you kid(s) hlp so it would be good bonding time too.