I used to consider a rental expensive, until I considered what it would cost to tow a borrowed (free) boat boat to the lake.
I would have to drive a 2nd car. Get the trailer ready, pack bearing etc.
Then I 'd have to pay to launch the boat and take the time to do it.
In the end it was much easier to just show up at the dock get on a rental boat and drive off vs. the challenges and expenses of towing my boat 6 hours round trip.
I agree renting a boat is expensive but there is a convenience factor to consider that makes renting tolerable.
For me renting has significant advantages vs. towing a boat from home.