You can go right to ebay they have so many for sale . The wanted price as follows Upper Deck appx $285 Bowman appx $60 Topps traded appx $25 those are the deal want prices for 1989 Ken Griffey JR in PSA 10 .
Cards from the 1980s aren't worth much. It also depends on the card company. Look it up online, but since it's graded mt 10, double the value of an ungraded card (at least)
When I want to know what something is worth, I like to go to ebay. And then I look to see what similar items have sold for. It does me no good, for example, to see that someone has an asking price of $200 on a card when actual cards are selling for $10. They're listing it with no actual intention of selling them. I've seen cards listed for over $1000 when actual selling prices are around $20. I can't even tell by looking for a Griffey rookie card under sold items because a number of different rookie cards were produced. The best thing I can suggest is to look at items that have sold and find the specific Griffey card you have. I performed a search for "Griffey Rookie Card" and specified sold items. 4700 sold listings were found. Just on the first page I found cards that sold from a low of 99c to a high of $225.99. So they vary widely. I am attaching a link to my search results. Find ones exactly like yours that have sold. That should give you a pretty good idea.
http://www.ebay.com/csc/i.html?_from=R40&_sacat=0&_nkw=griffey+rookie+card&LH_Complete=1&LH_Sold=1&rt=nc
Card made from 1985 to the present are usually not worth a lot...too bad I would have been rich..you should save it ...it may go up down the road...if you wanna check the price now..go to the Beckett card site....search it