A store that sells collectibles such as comic books and trading cards would be a good place to start. Also, there are books that come out yearly on the possible monetary value of baseball cards. These books are generally available at bookstores and in public libraries.
There are also links on the bottom of this page with links to questions that have been similar to yours have been asked. You might want to click on them and see what information is on them. I am sure that there are a lot of links to sites contained in the information.
Here is a search that you can click on and try in order to find professional grading services.
Professional Baseball Card Grading Service - Google Search
What are the specific cards that you have, please? It's possible that we might be able to give you some possible monetary values for them here on this site.
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