If you want to know a free ballpark number I would use
http://www.tuffstuff.com/priceguides or
http://sportlots.com/.
Tuff Stuff posts their 2009 catalogue. So, it is dated. But you will quickly find out which are the best cards in each set.
Sport Lots is actual sellers willing to sell their cards. You will be able to find most cards on there in a variety of conditions.
I like these both better than using eBay, since most cards are listed in both.