Ok let me get this straight...
There are now 2 versions of SIS, Elysium and Endurance. Elys is 5$ and Endur is 20$ (per update).
Elys is included in Endur. Future updates for each version will include the older version content.
So by skipping 3 or 4 updates and spending 20$ for days 18-20, I would get days 9-17 effectively for free.
May I suggest an alternative... an initial Elysium version price of say 10$ with subsequent updates being 3$ or such. Endurance being 20$ and subsequent updates being 7.50$. And to get the discounted updates you have to have paid for a full version.
And this of course leaves the question of is there a basic version that is still free.