@Annette33, if the hotel has to send a paid employee to the post office and loose an hour of paid work time there, which would happen in our post offices, 36 $ seems a reasonable price. If I charge my time correctly, I need to add at least 25 to 30 € for the post office trips. Plus postal fee.
For t-shirts, I usually offer send or donate to charity and so far everyone chose charity. I'd not ask sending an item that's worth less than the postal fee and if a guest asks for that, it's fee plus my time.
It's astonishing that they sent it your clothes. I lost quite a few items in hotels: my sister deposited my umbrella at the reception at departure and when I wanted to pick it up the next day, it was not there. A converter in a room: called, returned a few days later: no converter, a business leather bag, which I packed with our professional material for shipping and my collegue did not recognise and deposited at the reception. Again: call, drive there next time, no bag. It was a few weeks later, but we paid about 8 000 for the stay plus a few clients stayed there too. Maybe your report "they send a tshirt for 36 $ " is an incentive to book there 😉