What's My 1921 World Book Set Worth?

I have a complete set of 1921 World Book encyclopedias in good condition. My grandmother bought them in the late 1920s for my mother. The covers are all intact and have some really nice embossing, although the inside cover leaves on one or two volumes might be separating. But everything is complete and in generally good to very good condition, especially considering their age. There are no missing pages, etc. Nice illustrations. Gold leaf page edges, etc. Any idea of what they're worth, or a place where I can advertise them in case there's a collector out there? Thanks!

By Steve