Hi Michael, yes you can purchase the discounted upgrade version of v4 if you have any previous version of MoI. You don't need to pay full price again.

The discounted one is the second one on the purchase page: https://moi3d.com/purchase.htm .

Note that it says "Requires v3 license" in the page but actually any previous version license is ok. So you can get the v4 upgrade version if you have a version 2 or even a version 1 license.

Thanks, - Michael