The salary of people working and using those 'tools' this infrastructure is higher then 300$.

If your kubernetes cluster is part of your core infrastructure, then 300$ more or less should not be an issue at all (not to say that i think 300$ is nothing).

That should not mean that you should waste money but often enough, if you buy cheap and your hardware breaks and your time&material costs much more then what a better hardware would have cost, then you wasted money by buying cheap.

Unfortunate with IT products, there are certain things which are not directly visible: Like how secure is your product. GCP offers 2FA, Digital Ocean does not. How much money is it worth to you to have your whole infrastructure protected by 2FA? For me in a business context, non 2FA would be a no go.