I use mailgun and host lots of domains on my single account.

The cost for me is very low but I have lots of different hobby projects and charity projects I use so I really don't know at the moment what it costs to me

I use the Flex plan which might be hard to find when setting things up because it is the cheapest pay as you go plan. They are kind of hiding the flex plan option https://www.mailgun.com/pricing/


Free plan (no credit card required):
5,000 messages/month are included
There is a limit of 300 messages per day on the included sandbox domain
Data retention for Logs and the Events API is 1 day
You cannot create custom domains
You can only send to Authorized Recipients, and there is a maximum of 5 Authorized Recipients

Flex Plan (credit card required):
No daily sending limit
You receive 1,000 free messages per month. If you send over this amount, additional messages are charged at a rate of $1.00/1,000 messages
Data retention for Logs and the Events API is 5 days
You can create custom domains
You can add up to 5 routes
Use of Authorized Recipients is not required to send with custom domains; you may send to whomever you like!