I think it depends what goes into making the bag. We all know we can just stick the deck in a zip lock bag and be done with the functional part . But the tarot bag itself is a valuable and mystical part of the tarot experience in my opinion.
Many people don't understand what goes into designing and sewing things because they never have to do it themselves . And some really don't care too much what contains their decks because one thing is just as good as another to them, which is fine too.
But, other people like myself are very affected by fabrics and colors , and much like intoxicating scents they provide an energetically pleasing experience.
I charge depending on the complexity of the bag and the price of the fabric and embellishments , 5-20.00 ea.