List shamelessly based on Jadawin's.
Since lords and heroes cost are not shown, you do not need to do this for them, but nothing bad will happen if you do.

1. Open the mod in RPFM.
https://github.com/Frodo45127/rpfm/releases

2. Post a comment with these information for each unit:
{"unit_key", multiplayer cost},

Both can be found in mod/db/main_unit_tables

For example:
{"wh2_jmw_hef_inf_elven_warriors", 600},


3. Also post a comment with the updated unit name table:
land_units_onscreen_name_unit_key Unit Name (multiplayer cost)

It can usually be found somewhere in text/db. You could also do it directly into RPFM, extract that file and send it to me via discord PM (Maal#2043 in the modding or sfo discord).

For example:
land_units_onscreen_name_hef_inf_elven_warriors Sentinels (600)


4. In order the make the AI deal with high cost unit better, you can optionally do this for unit which cost 1000 or more:
["unit_key"] = {"replacement1_key", "replacement2_key"},

For example:
["wh2_dlc10_dwf_inf_giant_slayers"] = {"wh_main_dwf_inf_slayers", "wh_main_dwf_inf_longbeards_1"},

The first key is the custom unit to be replaced, the other two are units you choose that are suitable replacements (they need to be cheaper, and should have a similar role). Important: Both replacements need to be either custom units from the same mod, or vanilla units. Do NOT use any units here that are from a second custom unit mod!