Collect money for a music team retreat

You're in charge of activity planning for the worship band at your church and the annual retreat is getting closer on the calendar. The hassle of collecting the registration fees is looming. Your fellow musicians meet for practice every week in the midst of busy, busy lives and often can't be counted on to remember to bring cash or a check. You don't want to tax the worship budget any more than you have to, so you're looking for a solution that will combine the convenience of online payment with some kind of registration mechanism. So there's no more forgotten money and less work collecting registrations for you.