When using the Collect Money feature on sign ups, you as the group organizer (or Seller), will need to choose who pays the service fee equal to 5% of the purchase price plus $0.50 per transaction.
If you choose Buyer, your participants will be charged a service fee that is added to their total at checkout. As the seller, you would pay no fees to collect money on sign ups.
If you choose Seller, your participants will pay only the price listed on your sign up at checkout. The service fee would be deducted from the amount you, as the seller, collect.