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If you have an application which sends 10k messages per day to one receiver using SNS/SQS... then...
The sender pays 10k*31*0.06/100000 = $0.18 (18 cents)
The receiver needs to connect every 20 seconds: 3*60*24*31 = 4320. Then 134k. Then 10k messages to receive, and 10k messages to delete, for 31 days = 620k. You wont have this many requests since when you get a message, then you connect again, and not again until the next 20 seconds. You might get multiple messages from one request. So maybe it is 700k total.
This is (700k) * 0.01 / 10000 = (70 cents). Total price: $11 / year.
Not sure how this compares to hosting your own ActiveMQ. You have time to set it up, pay for servers / DB, backups, etc. And as you add more endpoints, you will need to scale it up. Not sure if you would have a support contract for ActiveMQ with a vendor.