What is an 1897 twenty dollar solid gold coin worth?

You need to know if you have "just a replica" or a replica bullion coin. Most replicas are made of plated base metal so they're only worth a few bucks. If it's an actual bullion coin it's worth whatever the gold it contains sells for at the current market price. If it's a bullion coin it'll probably have the weight and purity stamped on it somewhere. If not, it's probably just a cheap copy. Your can always check with a dealer or appraiser who can perform a purity test, if you want.