That’s a cool idea. Get the word around online, at local gun shops, ranges, and whatnot and who knows how many folks will use the service. There are guys who do this so it would be interesting to hear what they charge.
I pay young relatives $20/100 to anneal brass as a favor for them, but I don’t know what other people are willing to pay. $40/100 is as much as new 223 brass so that’s too much, but would be worth it for more expensive $1/ea brass, and on the top end of the price scale, oddball, hard to get, or Weatherby brass is often $3/ea new.
You have to charge enough to make it worth your while (plus taxes), pay to replace your equipment, then an extra 20% for hassles. I wouldn’t be surprised if half of new price is in the ballpark for small batches, and easy to get along with regular customers that anneal large batches could get a deep discount.
Hope it works out and pays for some powder.