The cost of the dye is only half the equation. The brush is where the retouching capital costs are involved. I have two spotting only brushes.

Windsor & Newton sable hair. One is 00 size and the other 000 size. Very Fine. Neither of mine cost less than $20 over 20 years ago.

The different dried spotting colours are dried in a 4 troughs of a 5 trough glazed bone china watercolur palette. The spare 5th trough is used for mixing dry dyes for matching toned print colours.

Yes, a tiny wipe of the brush on your tongue is all the moisture it takes to pick up a bit of dried dye.

I keep spoiled/test prints processed the same as finished prints to use for the first dab of the dye laden brush, and may dab a few more times to lighten the tone before applying spotting to the final print.