The cost increase is generally justified as an early business expense as 1) aws services are generally reliable, secure by default, and excellent uptime 2) cheaper than hiring a dedicated operations person, your developers can just cobble together something and go 3) you don't need to do capacity planning. database going underwater? convert it to one twice as powerful in about 15 minutes with zero downtime! magic
Capacity planning has to be done quarterly, you need good metrics to do that, then you have to order, assemble, test the hardware which for a one-off thing can be quick but as sustained business operations is a 2-4 week project from the initial request to having it serving production traffic. once growth levels off DIY datacenter stuff can make sense, but early stage with less than 50 employees the AWS premium makes a lot of sense. transitioning to dedicated hardware is also an indicator that growth has leveled off or become extremely predictable.