picture this: you got the spear and you need your hands but you have 40 blood points and you buy back your arm and hand for 20 so you buy the other side and then you have 0 blood
That would be useless! Why would you sell limbs to repair others? All you have to do is buy weapons and the game is still somewhat easy! Blood is so valuable, and even if you made it super cheap, it would be even more OP!