In 1.21 I grabbed ~300-400 levels (a lot as you can see), netherite pickaxe and started reforging it for good suffixes, suddenly got out of levels in 1-2 rerolls!
So I had to cheat in 10000 levels, reforge and throw them back, current costs are completely out of balance.
It was nowhere like THAT expensive in 1.20

The stock reforging level costs are the same as they were in 1.20

Modpacks can change them to whatever they please though, so you may encounter different costs.

No, this is not modpack. I just creted new fresh instance of 1.21.1 and anded apotheosis only, then default config is this:

augmenting {
    # The number of Sigils of Enhancement it costs to upgrade an affix in the Augmenting Table.
    # Synced.
    # Default: 2; Range: [0 ~ 64]
    I:"Upgrade Sigil Cost"=2

    # The number of experience levels it costs to upgrade an affix in the Augmenting Table.
    # Synced.
    # Default: 225; Range: [0 ~ 65536]
    I:"Upgrade Level Cost"=225

    # The number of Sigils of Enhancement it costs to reroll an affix in the Augmenting Table.
    # Synced.
    # Default: 1; Range: [0 ~ 64]
    I:"Reroll Sigil Cost"=1

    # The number of experience levels it costs to reroll an affix in the Augmenting Table.
    # Synced.
    # Default: 175; Range: [0 ~ 65536]
    I:"Reroll Level Cost"=175
}

I suggest you change those absurd costs to much reasonable or even zero, like there were in 1.20, its up to modpack developers to balance.

Those are for the augmenting table, not the reforging table. Those (again, configurable) costs were added as the Augmenting Table is a very-late-game block intended for arbitrary min-maxing. You can comfortably achieve the necessary XP costs using apoth-provided means (spawners, ancient knowledge, knowledge of the ages, pinnacle xp boost, etc).

If you have an issue with the costs configure them down.