Opals are kind of my thing, but I can't (literally can't -- I'm not being difficult) tell you what it's worth. Your miner has a value in mind and there's no way to know what that it unless he/she wants to tell. A jeweler can't tell you about your stone firstly because he/she is *probably* buying the more standard ovals and chatons, etc, rather than freeform cabs of matrix opal (which is what you have); and secondly, he/she doesn't have the stone in hand. It's __impossible__ to properly evaluate a stone's quality and potential price based on a photograph.
Personally, I'm not overly impressed with matrix opal in general as it can be brittle and the spots of color are pretty much fixed rather having the richer, more elusive "play of color" you'd find in another types like white or black opal. I have cut matrix opal and treated it myself so at least have had the stuff in my own grubby hands. (Or maybe that's having the grubby stuff in my reasonably clean hands.)
You could look around for opal-sales web sites that offer individual stones for sale for comparable stones -- but every company selling finished opals has its own pricing structure. One site quotes x-price for a 32ct stone, while at the next site you'll find a comparable 32ct stone for y-price. You could look at comparables on ebay for similar size stones that are drilled for hanging on a pendant (that appears to be what you have). HOWEVER -- those web sites typically don't deal in matrix stones because they're not as desirable as the other types of opal. The price should be lower than white or black finished stones as well.
Also consider that your miner probably won't accept returns if you decide the stone is not the quality described or size you want. The larger merchants are more likely to have standard returns policies. (I can't guarantee that but it's likely.)
Now, here's my two cents on how __I __ would prooceed. If the miner won't put a price on his merchandise, in my opinion he's playing games big time. I hope I don't offend anyone reading this but it has been __my__ experience that dealing directly with a miner is not a straight-forward process. Been there, done that, wasn't happy with the results but that was too bad for me. ((Ask yourself: "Would I buy a diamond from a guy who digs them up and facets them himself and _says_ they're high quality?"))
If the guy won't tell me the price I'd run away so fast his toupee would blow off into the dust. There are reliable merchants who don't play games. Unless I was standing in front of the miner with a loupe and a scale to personally evaluate the quality of the stone, I would walk away. The larger merchants have a better selection, a reasonably verifiable range of quality, and they'll be up front about their price. They're typically not going to indulge in price games or blow smoke about the quality or price of the stone.
Sorry to rave on like this. It's been that kind of day. This is __my__ answer to your question, and I'd expect to hear varied responses from other members of this group.
Good luck!
