To determine current worldwide market value of a record, you can check out completed auctions (not people's asking prices) on sites like eBay or Discogs. You have to be sure you are looking at the same artist, title, pressing, condition of record, and condition of cover as the one you have.
You have to take it into the store and let them look at it. What you could get depends on the condition and whether or not they have several copies already.
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