Yeah, acrylic would probably only be acceptable for "display" mantids. Or for wealthy people
I am having a hard time finding it lower than 6-10$ a square foot (you get one cage assuming dimensions are 6''x6" and you use an alternative bottom). But if you do start to offer these I'd be interested in what your prices would be. If you could hit the $10-15 range, I'm sure you could find customers, lol. Might want to get customers before making them tho (I've made the mistake of fabricating to much of one thing I thought was going to sell).
On a separate note, my brother use to "steal" art supplies from his college all the time. He made wire wrapped mineral necklaces to sell (trust me he needed the money). Not that I'm encouraging stealing... i'm just saying look into it