Typical credit card fees are 2.9% + 30c. Assuming that they have regular fees at not non-profit rates(which tend to be lower), it would make their average donation amount to be around $7.14

Source: 48995/689239 = (x*.029+.30)/x

With that many transactions they should be able to negotiate a lower fee than that. My company did a bit over 4 million in CC transactions last year and our rate is 1.9% and I believe the flat rate per transaction is 25 cents.

That's in the ballpark for monthly membership fees. ~$10/month.

As someone else pointed out 2.75%-2.9% is common, often thre is a charge per transaction too (on the order of 25cents after it's all said and done). The fee can change based on the card type (the merchant pays a higher fee on rewards cards normally...someone has to pay for rewards!) and international purchases can have additional fees. Charges backs can also bump up fees, ditto for outsourced fraud protection.

2.9% is fairly standard with Stripe et. al., but fees from things like chargebacks could probably add up to another 1%.

Maybe it includes unfavorable (normal for credit card xactions) exchange rate conversions?

My understanding is that credit cards give you the best exchange rates available at retail.

Some banks do tack on a foreign transaction fee though, but that goes on the payer.

Aren't these generally dumped on the person paying?