Honestly, specimen opal is quite affordable! These cost me anywhere from $12 to $50 each. The opals that cost a "fortune" are ones that are jewelry-grade.

So if you get an opal that's already dried out and it's full of color and opal "fire", it's more than likely considered to be "stable" and putting it in water to store it could possibly make it "unstable" (dependent on what type of opal it is)

Not ALL opals should be stored in water, only non-hydrophane opals are "safe" to be stored that way. Hydrophane opals can readily absorb significant amounts of water and also have the ability to dry it out, BUT there is a chance that they may become cloudy or transparent and lose their opal "fire" permanently. The Ethiopian Opals I've posted here are all NON-HYDROPHANE opals and these ones in particular MUST stay in water, as the conditions they were mined in were wet. Drying them out would likely cause them to crack or craze. Australian opal is also considered non-hydrophane but it will not be altered if submerged in water. You *can* put it in water if you want to (it won't absorb it), but it's unnecessary to do so. I'd be very suspicious of any opal vendor that sold jewelry-grade opal that was submerged in water. You have no clue if it is going to crack or be cloudy when dried out.