Only if you are pushing 1 message per write. 1 write per agent per minute, ends up at just over 2$ per month fox 10 agents, regardless of the number of messages - it's cheaper for any setup I've encountered. AWS services are always middling solutions, which you can often optimize for better cost efficiency.
What constitutes "the queue" is a matter of data structuring, not a singular brand (eg RabbitMQ, Redis, SQS, etc each have their own internals).
Any middle tiering of the data before it reaches the consumer, is still "the queue". You don't need to know the internals of SQS, anymore than a consumer need know the black box elements of how you collate the messages within your ad-hoc queue.
