It's €56.80 due to VAT on the €21.99 at least.
Wouldn't be surprised if the MID and PCI DSS charges are VAT liable too.
Dividing this by 300 transactions it comes to 19c a transaction minimum.
Using the €50 + VAT for 500 transactions it comes down to 18c a transaction.
The added Interchange, Scheme, etc, etc fees are a bigger worry since we don't have figures on them.
In a sense this equates to being charged for
1) Having online payments
2) Having cards associated with online payments
Clearly cards are integral to online payment systems so we are being doubly charged for using cards online.
I think I'm starting to see

what Stripe may have on the merchant services here.
But it's hard to quantify the margin without actual hypothetical transaction lists and fees.