Actually all Affinity software is 50% Off. Directly from Affinity or through the Microsoft store.
https://affinity.serif.com/en-us/store/
https://affinity.serif.com/en-us/store/
There is no upgrade, if you already own Affinity Photo, you've got the latest version.Which version is this? Can't tell from the website.
edit: near as I can tell this is the same version I bought in 2017.... Is this the sale before the upgrade?