Who Should Pay For Parents 5oth Anniversary

My parents 5oth anniversary is this summer and I, my 3 sisters and my brother are planning the event. However, they are not very happy dividing the costs between the 5 of us. I do not think that $ 650.00 divided between the 5 of us is asking for much, considering how much are parents have done for us. Anyhow, I just wanted to know if it is ethical to ask for family and friends to sponsor our parents 50th anniversary. They want to ask for sponsors and I feel very embarrassed by this, because I feel we should pay for the entire cost. Am I wrong? Please help!!!