You can add a "Split" to any of your groups, similar to the way you'd add a location or a photo. Add the total price, and anyone with a credit card can chip in. They just click the "chip in" button and their card number. Price is divided equally, and the more people that join, the more the price drops. Which, duh. Once you're ready to cash in, just click collect and after entering in your bank account info, GroupMe says you'll see the funds within 24 hours.
There is a slight catch—starting March 11, split contributors will be charged 4 percent plus a dollar fee, for credit card processing and a "convenience charge" paid to GroupMe. That's a little annoying, but less so than hounding friends endlessly to pay you back for concert tickets you bought months ago. [iPhone, Android via GroupMe]