I’m not quite following what you wanted to say in the last.
If you look at the initial comment I’ve pointed you to the transport documentation. Specifically, factories and clients. Concurrency plays a significant role as well and can be configured if needed. The snippet you’ve shared is using all the defaults. So for a 4 cores CPU concurrency would be
max(Number of logical processors,2), eight.
Looking at the calculation, I’m not sure how you’d be paying $300 dollars. Assuming that with the given configuration that has 6.5K operations per 12 hours, it would be 13K operations per day, or 390K operations per month. Given you have 13 million free operations per month and low message flow, I’d imagine your bill would be substantially lower than $300. Even when you process messages, on average a message would be 3 billable operations. Something doesn’t add up. Unless you’re running a very big number of endpoints / scaled-out instances.
Also, like @bording pointed out, you should disable the legacy satellite. That with tuned performance to match your need would lead to a substantially lower bill.
And last, but not the list, if you find your solution indeed requiring such a significant resource allocation that your bill is getting over $300+, perhaps it’s worth looking at Premium tier. I’m not convinced it’s the case, but once you see your spend and it proves to be as you estimated, for ~$600/m you’ll have designated resources and no pay-per-operation.