What country? The upgrade price should be about €75.
And yes LR6 does include support for the 5DS.
I think you have selected to buy 2 full versions or 3 upgrade versions. Cancel out of any web page you are in and try buying it again. Look in the shopping cart and delete, remove, all other copies except one.
After you choose to buy then you can indicate that you want to purchase an upgrade. Then, after you have indicated what version you are upgrading from, the price will change to the upgrade price. Have you done all that?