Antique or vintage record players vary in value based on condition, demand, and location. In general, there is a large inventory compared to demand as older people downsize and flood the market. Learn more about your particular item by describing what sort of record player it is; electric, wind up, midcentury cabinet, etc. Look for labels to see who made the player. You may find the name of the model as well as the serial number. The more information you have, the easier it will be to understand the value.
If it was made by Victor Victrola, for instance, you can check out the Victor Victrola site which features information on models, serial numbers, finishes, and veneers, etc. Several online forums discuss old record players but it's best to visit these sites armed with a little information.
Also, check out your local Craigslist or Facebook marketplace to see what you record player sells for in your area. Many people prefer to sell locally due to shipping costs. It can be easier to sell direct