Happy to help out on the value / money / rarity question! And I am attracted to old bottles for all of these reasons, the history, the fun of holding a 100+ year old artifact, the fun of the hunt to find bottles, and the monetary value.
This answer may be a bit general but should fit most bottle categories... probably the most valuable old bottles are from these categories... Western Whiskies and Western Bitters bottles, along with the early East Coast colored Historical Flasks. Select bottles from these categories have changed hands privately and at auction for over $100,000 each! Yes... that much!
Being located in a relatively newer part of the country, we rarely find Historical Flasks out here. In years of digging, I think I know of only a couple of people who have found the most common ca 1860's Double Eagle historical flasks, and they were found in the early settled towns of Walla Walla and Port Townsend. The early pre-1860 Pontiled bottles are rarely found out here, again, perhaps Port Gamble, Steilacoom, Walla Walla, Port Townsend etc are where they have turned up.
Bottle diggers and scuba divers do have a better chance of finding good Western whiskies, from San Francisco, or even Washington Territory embossed drug store, soda, and whiskey bottles. Some good Western bitters bottles have been dug here also, but again, our area is just a bit too recently settled to get the good early Western bottles. San Francisco / Gold Rush era California towns have produced tons of valuable bottles that are rarely found up here in WA State. I have heard of early bottle divers finding great stuff off of Port Townsend... whiskies, Washington Territory bottles, and good stuff that was dumped overboard off all the ships that cleared customs there, or were doing commerce between WA and CA. Ditto with Port Gamble, Port Blakely, Roche Harbor, and other ports. I think there are still very good bottles to be found, but location is critical, and diving off early ports and territorial settlements would be about the best chance. Some good Western Bitters bottles have been found diving off the early WA settlements, some of these are worth $50,000 or more!
Having said all that, there are still bottles in the $20-$2000 range that do turn up a bit more frequently here in Washington. First of all, plain unembossed bottles are rarely worth much at all. So, look for embossed lettering. And another general rule... screw top bottles are pretty much "recycle" items and not collected. Look for the early embossed Hutchinson (blob top style) soda bottles, they exist from Wash Territory and WA State and are worth $20-$500 each. Look for embossed clear and colored pharmacy / drug store bottle, from WA Terr days all the way thru 1915 there are some good and rare bottles, again, valued from $10-$500 each. There are very pretty cornflower blue Seattle W. T. druggist bottles that are valued at $500 each or more. WA state embossed whiskey flasks and cylinders can get valuable. They are currently priced from about $20 - $2000 or more each. Probably the most valuable would be a clear whiskey fifth, embossed from M & K Gottstein of Seattle, W. T. (WA TERR) with embossed Indian paddling a canoe. The old J H CUTTER whiskies from SF CAL were used quite a bit up here and come in many varieties, some of the rare early Applied Gloppy tops can be worth $2000! Bottles from where I live up in Bellingham, that have the names of the earlier towns here like New Whatcom, Sehome, Fairhaven have a great local collector value, and are kind of ghost town bottles. Some good bottles from Portland Oregon have been found in the Puget Sound area. And pick up Canadian bottles, the stoneware Ginger Beer bottles from British Columbia can be worth $100's each. The best bottle from BC is a stoneware stenciled Cross & Co Black Bear Brand ginger beer bottle, with stenciled Standing Black Bear animal! Worth about $1000 or more. Bottles from Victoria BC are good too! And don't be afraid to pick up old power or telegraph glass /porcelain insulators. There were some historic 1860-1880 telegraph lines that ran thru Washington, and some of these early insulators in cobalt blue, sapphire blue, or greens can be worth $2000 or more. The names to look for are Cal Electric Works, E C & M CO SF, Tillitson (threadless insulator), S McKee (threadless) and a few others.
So, don't be discouraged, the rare bottles are rare for a reason, and valuable. It takes perseverance to find good ones, just like digging bottles. I think diving is pretty much wide open for more good finds and discoveries, unlike land digging where some towns in WA are pretty much "dug out." Good luck and stay safe, and I hope to see some good bottles showing up on this thread!