Coins Before The 1800's

The Krause world coin catalogues go back to 1601, although for some countries and states, only the crown/thaler/dollar sized coins and the gold coins are listed.

For coins either not listed in Krause or issued before the Krauses begin, your best bet is world auction prices realised databases. The one I use is CoinArchives, which has an Ancients section and a Medieval & Modern section. The search function is a bit unwieldy, but quite powerful once you get the hang of it.

Note that CoinArchives prices are mainly sourced from "brick-and-mortar" auction houses in Europe and elsewhere; several of these auction houses have reputations for getting coins "bid up" well above estimated market values, so take any prices realised there as the maximum a coin might be worth, not an average. You certainly wouldn't get that kind of money selling a similar coin on ebay or over the counter to a dealer.