I didn't try to hit that because that's harder to call, especially at a small startup. If what is probably "the guy doing all this" happens to be more comfortable with k8s than the AWS stack you can end up winning by going with a nominally more complicated k8s stack that doesn't force you to spend dozens of hours learning more new things and instead just using what you already know. For a small startup those training costs are proportionally huge compared to a more established larger going concern already making money. Startups should generally always go with whatever their engineers already know unless there is a damned good reason not to. (And "I just wanted to learn it" is not a good reason for the startup.)

But monetarily, even for a startup, $400/month savings is something you shouldn't be pouring the equivalent of $5000 (or more, just picking a reasonable concrete number to anchor the point) into. You really need to solve a $400/month problem by putting your time into something, anything that will promote revenue growth sooner and faster rather than optimizing that particular cost.