That pricing seems typical. Don't forget to value the convenience of not handling cash, chasing up payments etc.
What are your typical transaction amounts ? And how many of those a month?
Will your payments typically be with the cardholder physically present, or typically online?
If cardholder present, there will be some new "tap on phone" solutions coming out that allow higher end phones to be used as card terminals, without additional hardware. These will be subject to the €50 contactless limit, unless ApplePay, AndroidPay or some other xPay are used.
Revolut and N26 don't currently offer accounts to charities, but this may be a space to keep an eye on. If you and every payer had e.g. a Revolut account you'd get free instant payments and a realtime confirmation if they paid in front of you (just don't keep large balances in the likes of Revolut).