Additional Gift economy Option

I do not see a way for others to make a donation other that a three month option to pay 30 monthly or 95 monthly. Can we agree to list a donation that can be any amount?

To learn more about the gift economy option: https://www.ted.com/talks/alex_gendler_what_is_a_gift_economy?utm_campaign=tedspread&utm_medium=referral&utm_source=tedcomshare