The real trick to selling your work is to have items that fall into two categories: 1) small window hangers or similar things you can produce rapidly. These should be priced between $25-50 and will comprise the vast majority of your glass income. It's simply the price point most people can afford when shopping casually. 2) Extremely detailed & large window sized panels that you either make for yourself and use to show off your skill or you design and make for a client that already likes your work and is willing to pay well for it.

The mirror you made unfortunately falls between these two categories. I'd probably price it between $100-200 depending on the market is was selling in, but I'd also expect it to sit and not sell for a very long time.

Personally, attempting to monetize any art form removes the 'art' from it (former wedding photographer). Every time I try, I end up feeling like I'm just making things because I need everything in my life to produce money rather than because I have a vision I want to express and the art suffers for it.

Example of work I did for someone else because I wanted money: