"do not try to insult others, because you even can't follow yourself"
What did you smoke today?
Your arguments are only supporting mine. Go outside and chill, please. I'll gladly follow, but please read the below first:
PCBWay is reporting me $51 for 100x100x4, JLCPCB is reporting $28 for 100x100x4 and even with DHL Express shipping included, I am still below the price of PCBway. Not sure where did you smoked out those 28$ for PCBway.
If PCBWay would be cheap, I'd have probably used it in the past - didn't happen, because it never actually was cheaper for any boards I did in the couple years back.
Maybe you see different prices, but I work with what I got. (Mainly through PCBshopper. And if some manufacturer happens to report incorrectly, sorry to them, but not my issue. I have also tried switching different countries, including EU and US. JLC still way cheaper, than your PCBway, for your original 100x100x4L suggestion.)
In any case, with any of these prices, I still do not see why an inexperienced designer shall push 0.8 pitch BGA on a small PCB, as hs first 4L design. That is not likely to happen. Any of these prices are more than likely couple times below what would a local pcb fab quote for a single prototype PCB.