Facebook won't allow numbers to be given, but if you read between the lines of various CppCon videos a 0.1% speedup in some of their core algorithms can make the costs go down by several hundred thousand dollars a year. A lot of that is the power bill because they don't need to run the AC is much to keep the data centers cool. (they also need to buy less computers, and less air conditioners to keep them cool, and eventually more building to keep the computers in)
You can’t answer this question without both a technical design and projected user behavior/access patterns. And I don’t think you’re going to get data on this from these platforms themselves. Unfortunately, this question is impossible to answer in this format. If you want to build a “clone”, first design it and then estimate the costs of that design.
Probably better off using a service like https://bunny.net for cdn and storage.
Your first cost saving is avoid AWS unless you want to bankrupt yourself. They're great for backups but bandwidth costs will kill you.