Excel 2007 : Sum amount for different appereance

I'm using excel to break down registration statistics for a series of events I am hosting. I would like to see how much of my total event registration income comes from regular attenders--those who registered to attend multiple events--versus those who just registered for one or two events.

I began by the FREQUENCY function to see how many people registered for 1, 2, 3... events (signified by their registrant ID appearing 1,2, or 3 times in the registration column). This worked well enough; however, I ran into trouble when I began sum how much these groupings paid collectively (IE, how much money I received from those who only attended 1 event). After some research, it appears that this is because the FREQUENCY function returns a 0 after each occurrence of the same value after the first.

Does anyone have an idea for a function that solves this? I have attached an example of this scenario with question marks signifying the cell I am trying to fill with this function.

THANK YOU!