I read one of the older issues that says that you need to edit both the client config and the server one but still it doesn't seem to do anything. Even when going singleplayer and changing the config, the number of levels required always stays the same.
I even tried to change the function type. I tested with the same item every time but the amount always stayed at 17 levels.

An easier way to make everything cheaper would be great, or at least some documentation on how to do so.

Here is my current config.

{
  "allow_removing_curses": false,
  "dedicated_server_options": {
    "alternative_cost_display_enabled": false
  },
  "client_options": {
    "show_enchantment_cost": true
  },
  "disenchant_to_book": {
    "enabled": true,
    "consume_enchanted_item": false,
    "cost_function": {
      "function": {
        "type": "grindenchantments:count_levels"
      },
      "factor": 1.0,
      "offset": 0.0,
      "type": "grindenchantments:transform"
    }
  },
  "move_enchantments": {
    "enabled": true,
    "cost_function": {
      "function": {
        "function": {
          "normal_factor": 1.0,
          "treasure_factor": 2.0,
          "type": "grindenchantments:count_levels"
        },
        "type": "grindenchantments:first_enchantment"
      },
      "factor": 0.5,
      "offset": 0.5,
      "type": "grindenchantments:transform"
    }
  },
  "version": 2
}

I agree, by default everything is a bit too expensive. I had the same problem and came to the GitHub to see if there was a way to tweak this.

Do you see any related errors in the log (.minecraft/logs/latest.log)? If any error occurs while reading the config file, the mod is just going to use the default.

Also, what Minecraft version are you on? This looks like an older config.

An easier way to make everything cheaper would be great, or at least some documentation on how to do so.

Yeah, this is severely lacking in that regard. I plan on writing some documentation at some point, but until then, there's not really much other than this comment on another issue.

you need to add

   "disenchant_to_book": {
   ...
+     "normal_factor": 1.0,
+     "treasure_factor": 2.0, 
      "type": "grindenchantments:count_levels"