I'm finding the difference just between Sonnet 4 and Sonnet 4.5 to be meaningful in terms of the complexity of tasks I'm willing to use them for.
Is there a digit missing? I don't understand why this existing in 5 years is absurd
Depends almost completely on usage. No one is renting out hardware 24x7 and making a loss on it.
If you only have sporadic use then renting is better. If you're running it almost all the time of purchasing it outright is better.