It absolutely depends on how burst driven your utilization pattern is, but don't forget the cost to actually manage the test cluster, and the engineering cycles that go into optimizing and sharding those tests across the cluster.
For sure, lots of considerations to take into account. If you're already running your own CI pipeline though, tests on top of it are trivial (in my experience running a Jenkins CI pipeline for a python monolith). Tweak your test runner, upsize the EC2 instance, and go grab a mojito.
