I'm guessing time is short as the season is just about over, so here are two pretty good ideas. If any of the girls (preferably all of them) know what college they will be attending already, tshirts with their new school's logo were a huge hit for my daughter's softball team last year. In addition the girls gave smaller items in their gift-bag, like a bag of candy or assorted candies from the store. Maybe for the girls who are undecided (or aren't attending college) a gas gift card would be good.
The second idea was great for my daughter's volleyball team - this one might take a tad bit more planning but again, was a big hit. The juniors made each of the girls one of those no-sew flannel blankets. On one side they had the girls favorite sport team (my daughter's was the Cubs) and the other a complimentary pattern (she has it at her dorm and I don't remember the other side) like zebra, polka dots, or a favorite solid color. They were so cool bec. the girls all knew each other so well, that it (even now) brings a tear to your eye. There was the girl who really was into penquins instead of a sports team and another who liked flamingos. The instructions are online just do a google search.
My other daughter made one of these for her boyfriend for Christmas and it cost her about $25, I think (the fabric stores always have coupons in the paper). Good luck and have fun putting everything together!