Server costs will certainly go down as Give A Dime reaches scale, but will always be necessary per user to account for bank transaction requests and other services. I will update the FAQ to be more clear on how we use this fee. We also intend to use those funds to continue growing and vetting charities in other communities.
We asked a lawyer if we could be classified as a 501c3, but it didn't seem possible given what we do :-/. Instead, we're looking to be classified as a B-Corp in the future.