That reminded me of a project where person leading it estimated that it will be cheaper and faster to use AWS, they only forgot all the hidden fees that AWS add

That reminded me of a project where person leading it estimated that it will be cheaper and faster to use AWS, they only forgot all the hidden fees that AWS adds, most commonly the network fees (which are charged between AZs) or EBS etc. On top of that an instance that claims to have specific parameters won't deliver the same performance as supposedly equivalent physical machine, so you will need to use bigger instances etc. Ultimately the project did not have resources to set up DR version which was originally planned and still went way over the budget.