If you rent a train for a kid like mine, he may never be willing to give it up
I have done my toy shopping at (mostly) a few good thrift shops, toy store after-holiday clearance sales, online clearance sales, Tuesday Morning store, etc. We have gotten good stuff like BRIO at 10-50% of retail by looking in the right places, at the right time. Tuesday morning has wooden toys *even now*.
The travel etch-a-sketch, for example, goes for less than a dollar locally.
So finance wise, I am not seeing any benefit to the rent-a-toy. A wooden toy swap in your area might be another way to go. (you organize it!) Check the Target after-Christmas sale. If you go at just the right time wooden toys will be 75-90% off.
This does not address the environmental aspect, but I think local re-use and sharing is the way to go