If I were doing it on my own account my estimate is close to yours. I have a cloud-native email newsletter system I built already, hooking up a payment gateway is routine, testing can be a bit of a hassle.

You could put a job like that up on a freelancer platform for a lot less money and you might get a good outcome or you might not.

My figure would assume there is a certain amount of arguing and barguing about requirements and that you’re dealing with somebody who will really come through, dot all the i’s and cross all the t’s and it is worth it if you are really making money on a newsletter.