What is the issue with having mega power fists buyable from the npc's if the same npc sells you mk3 armor and 50 cal BMG rifles?
However as those fists can easily kill you, so they are viable in pvp, I think a high price is fine.
The issue isn't that MPF is buyable, people are selling them to the vendor for insane amounts. You can make 3 mega fists for under 1000 caps and sell/trade them to the heart vendor for a rocket launcher or however many caps he has. I have seen some people just camping the vendor all day buying out all the materials and robo hands and constantly selling MPF for huge profit. (the same people who are buying robo hands for 150 each all day even though they could easily afford to pay double that). I would like to think this is a bug and not intentional.