It's not at all unreasonable...40$ or so seems to be about the going rate.
As for a plug kit.... Hmmm... good to have in a jam but should be for temporary use only...
I used to be a Tire Buster at a few shops and recently quit selling auto parts... we supplied garages with their tire repair supplies... as far as I know the only legal tire repair in Ontario on LT or P or ST series tire is a Combi-Patch or Patch/Plug....
Looks like this...
Garages might sell the unit for 10$ or more depending on the size of the puncture..
40$ or so is worth it.. consider that the tire is re-inflated,dunked in a tank to find the leak/s, deflated, put on a machine ,taken off the wheel, put in a Tire-Vise , puncture hole is reamed and ground down from the inside, cleaned , adhesive is added, the 10$ or more Patch/Plug is pulled through the reamed puncture hole and stuck onto the adhesive and is then passed under a variety of rollers.... put back onto the wheel..re-inflated, dunked again in a tank.. and put on another machine to balance it....
And as mentioned above... if you bring in a car-less wheel/tire the cost would probably be cheaper.
Randy