offer it up to local pinball owners. there's always someone that needs a sheet a glass. if your old sheets look like new (no scratches), most people wouldn't bat an eye and might even flip you $10 per sheet of glass. that's still cheaper than purchasing it at a show.

I purchased 2 sheets of PDI glass a few years back at the chicago expo and have used one sheet in a game so far (metallica).

the glass is truly eye-opening amazing, however it does appear to be very easily subject to scratching easily and I'm careful with my games. they remain covered when not in use, I use a light swiffer to remove any surface dust before cleaning with a new micro-fibre cloth and the cleaning fluid that I purchased with the glass.

I just wish that the coating was a bit more resilient.