I only need Rhino a couple of days, sometimes weeks per year. That’s why I am still using version 3.0 with Flamingo 1.1. I simply cannot justify the price for an upgrade.
How much would I like to pay, I was asked by @brian. Well, as little as possible, of course. Ideal would be a graded (?) hire purchase plan: In the beginning price per hour is high, then after usage for say a 100 hours it drops, until finally one gets a full license. That would give a high incentive to using Rhino and paying for it (as opposed to pirating it).
Concerning a rough price estimate, and not graded yet: Let’s say, for people using Rhino for more than one year intensively, it should still make sense to purchase a full license. That is 52 weeks of 8 hours per work day usage, so 52 × 5 × 8 = 2080 hours, or approximately 2000. With a purchase price of roughly 1000 USD, that leads to:
1000 / 2000 = 50 cents / hour
The basis for the subscription could be an Internet wide Zoo, hosted by McNeel.