@High Seas,
It will be in fits and starts. I have three different websites that I'd like to get this started for. They all have slightly different things going on but none of them will be on the scale of daily transactions.
Website 1: Occasional event tickets (3-4 times a year), donations, memberships. Average transaction probably in the $20 range. Maybe 100-200 transactions total per year, clumped around events. This one is most pressing.
Website 2: Merchandise, donations, memberships. Average transaction probably in the $15 range. Maybe 25-50 transactions per year.
Website 3: Merchandise, donations. Much broader membership but probably less merchandise/ opportunities to pay for things available. I'd guess an average of... $10/ transaction with maybe 50-75/ year.
I did see that Paypal offers reduced rates to nonprofits. I'm not sure about website #3, but both website #1 and #2 are nonprofit organizations. The reduction isn't huge -- rates start at 2.2 percent instead of 2.9 percent (I think, I'm sure of the first but not the second).