Don't worry about the registration fee. It serves to eliminate people who are not serious about participating/developing their startup plans. You should register (with $199), and if you are serious about your plans you'll have many, many opportunities to get your full $199 back from MassChallenge. They make it easy to get reimbursed (e.g. give an informal pitch in one of the early pitch practice sessions, etc.). Last year we got our registration fee back very quickly (we could have gotten back even several times that).
Olivier Boss, Energesis Pharmaceuticals (a MassChallenge 2010 award winner)