Organize money for a birthday party

Your husband's finally leaving his 30s and is hitting the big 4-0 next month. You want to throw him a big party and invite a lot of friends and family, but you want it to be a surprise. You start getting the word out quietly, but find that people want to chip in financially to really make it a great party. You realize it'd be great to be able to collect this help and get a head count at the same time. But you don't want the hassle of keeping track.