Unfortunately 1990 Score Football cards are not worth much of anything. You'll be lucky to get a dollar for one card. Even a Joe Montana card is only worth about $1.50 from the time. The problem is that cards during that time were mass produced which means they aren't rare. I hope I don't hurt your feelings with bad news, I'm sorry. I hope you keep collecting because cards today can be worth quite a bit because there are rare autographs and memorabilia cards. I hope this helps you!
Some of the valuable 1990 score football cards include Reggie White AP that had a value of $37.45 and Jerry Rice AP of $31.00. There were also the Junior Seau RC Rookie card that has a value of $13.99 and John Elway of $9.00. You can get a list of the 1990 score football cards from http://www.comc.com/Cards/Football/1990/Score.