Using the anvil is "too expensive" with simple enchantments

I try to enchant a diamond sword with sharpness V, Looting III, Mending, and Unbreaking III, and combining just mending and unbreaking on a single book with a sword costs 37 levels, impossible with all 4 enchantments, I thought that's just how it is, but my friend tried to put just Protection IV on his iron chestplate and it was "too expensive"