The dates are from mid 1970-mid 1990's.Full unopened sets, partial ssets, plates, collectibles, etc

Based on the years you speak of, only a few items would have any valus (over $10 a card or over $40 a set).

Just to get a ball park idea there are some online price guides.

beckett.com is one
tufstuff is another

Ebay is a good place to see what people are acutally getting for card which is almost less then what any price guide says.

The cards you would want to look for in your collections are:

From the 70's
1973 TOPPS Schmidt Rookie
1975 TOPPS Robin Yount
1975 TOPPS George Brett
1979 TOPPS Ozzie Smith
1980 TOPPS Rickey Henderson
1982 Topps Traded Cal Ripken Jr
1984 Donruss Don Mattingly
1984 Fleer Traded Roger Clemens
1989 Upper Deck Ken Griffey Jr


Those are basically the only cards worth $50 or more in very very very nice condition (and yes, I mean very very very).

I hope that helps and if you need more help, please email me.

Go to a sports cards/collectible dealership. Ask them how much it is. If they ask to buy it, its probably worth more then they are telling you.

ebay

You could go to a memorabilia store, Steiner Sports, or eBay.