It depends what condition the cards are in. Are they fresh out of the pack despite being 30 years old, or do they have dog eared corners with white showing? Is there any warping, dings, scratches of any kind?
I am a baseball card guy so basketball is not my forte, but likely most of these cards likely are not worth the paper they are printed on.
Check completed eBay sales for the full sets on eBay, or have a glance through a consignment site like COMC.com. A quick search of
1991 Skybox shows some cards from this set have value, particularly Team USA. Anything Michael Jordan is worth hanging onto. Each set should have some key rookie cards which are very popular these days.
If you want to recoup $20, take them to your local card store. You'll also get takers on Craigslist or Facebook marketplace. If you want to put in a bit more legwork, package up the full sets and sell them on eBay, again check comparable sold prices. Getting key cards from these sets professionally graded is a step to take if you are very serious and have some disposable cash laying around, but I wouldn't recommend this initially.
