Artillery team member here. "Rather pricey" really depends on what you compare it to. Artillery Core is free. Artillery Pro costs money, but it runs directly in your cloud environment, so it's extremely cost effective compared to hosted SaaS solutions. We designed it for large-volume use, especially in CI/CD pipelines. There are no limits on test minutes, vuser concurrency, number of tests you can run etc.
Can you DIY a solution that will let you instantly scale up from running tests locally to running them on 500 workers in any of 13 different geographical regions? With no servers to manage or maintain whatsoever. Sure you can, but it's not the best use of time for a lot of teams.