Market rate is good but also or mostly: do. The. Math.
Figure out how much this costs you. How much time and what is your per-minute shop cost. If you don't know your hourly COST (then divide by 60) start there.
LOTS of businesses screw up these cost analyses. It is why restaurants go out of business. They don't accurately run costs, so are confused as to where the money goes.
A good specific example is the belief that credit cards are expensive because of the fees charged. But do the math. How long does it take to accept cash vs them swiping a card? How much to balance the drawer at end of day? How much time and gas to drive it over to the bank? Etc. Oh, it turns out it usually costs more to accept cash than cards, it's just a hidden cost.
So: don't accidentally, secretly, loose money doing this.
A place down the street from me used to be my go-to shop and they happily did transfers, for pretty good prices. Like... want to say $35/45/55 based entirely on size (shipping mostly), add $5 for NFA, and that was WAY lower than others because: they had an office guy who only did this. Comfortable on the computer and familiar with the rules and laws so fast at it, no rework, and only in the back office so no retail walk in to distract.
They did this so much that when he was out for vacation or so on: no transfers. They would NOT ruin their model by having to flop between retail and paperwork. So, also keep in mind that processes are there on purpose, stick to them or again costs will spiral out of control without you noticing.