I would find $25 reasonable, if I had to go to a UPS store and buy a box and pay shipping it would probably cost about the same, if not more.

It would be nice if they would just send you a shipping container, prepaid to return it in, but I think those days are long gone.

They are fairly clear what the terms are

you can send or bring your bag to a local Authorized Repair Center. No repair number is needed. Please note that you are responsible for any freight charges incurred when shipping your bag to an authorized repair center.

By the way, you did not spend money on a free repair. You spend the money to ship it to a repair center. Had you brought it to a repair center instead of the dealer, there would not have been any charge.