tg

Okay so the more times an item has been through the anvil, the more it can cost to put it through the anvil the next time
This cost starts off pretty low (an item on its second time will only cost 1 extra level) but goes pretty high quickly (an item going through the anvil for the 6th time will cost like 65 extra levels)
Also, you can't cheese the system by combining a fresh item with a book that has been through an anvil a bunch
being put through an anvil is called a working
So what you want to do is start off with a new ember rod (0 workings) and a book you enchanted on the enchanting table (0 workings)
Combine these together to get an ember rod with 1 working
now when you put items through an anvil, the most efficient way to do it is to use two items with the same number of workings
so enchant two books on the enchanting table
and anvil them together to get a book with 1 working
Merge that with the ember rod and you should have a minimum of 3 enchants and a rod with 2 workings
now rinse and repeat. Now enchant 4 books on the enchanting table. merge two of them together to get a book with 1 working, and merge the other two together to get another 1 working book. then merge those two together to get a 2 working book
the best way i can explain this is to imagine you're combining four looting I books into a Looting III book, do it in that order
then merge that book with the ember rod, you should have a minumum of 7 enchants and a rod with 3 workings
then enchant 8 more enchanted books and merge them together like you're making a prot IV book out of prot I books (same way as above)
then combine that with your ember rod and you should have literally 15 enchants if you had the worst luck possible and only got 1 enchant on every book
and the cost should never go over 70 levels
if you see a high cost it's because the enchants themselves are adding to the cost, but it won't affect the cost of future upgrades