Enchanting is too expensive

while enchanting a diamond helmet with:
Protection IV
Respiration III
Unbreaking III
Aqua affinity I

and a Diamond with:
Sharpness IV
Knockback II
Unbreaking III
Looting II

is impossible to repair. Both with other diamond gear and single diamonds.
This is needles to say annoying seeing that i allerady have used many diamonds and levels to get my gear this far.

i am also wondering what "too expensive" means, is this anything that costs over 40 lvls? 50 lvls? you can get over 100 lvls killing the ender dragon so... i don't know...

(My sword still needs to be enchanted with fire aspect II and sharpness V to be the strongest sword in the game)