I have always purchased the latest version but it seems quite cheap this year as in previous release cycles, particularly when upgrading from an older version.
Well it usually give up to 35-40% off in august-september somewhere for 10.0 - that would be as 10.5 is about to happend.
But it varies depending how old version you upgrade from.
And if you buy then - and wait to activate license until oct-nov - you get a grace period upgrade for free to 10.5.
Last and this year - it seems new release is november rather than december for years before that.
That is if being gready.
But I’d say that 20% of new price to major version upgrade, and 10% if minor version upgrade - if keep upgrading - is pretty decent.
It used to be much worse.
So if you want it - just get it.