Thanks for your continued support, it’s most appreciated. You could upgrade your next site individually or if you plan on using Ultra few times, we have a developer multi-site license for $50 (unlimited).
You could upgrade from Appearance > Themes > Ultra Premium if you have the free version installed or buy a license using the buy button on this page: https://purothemes.com/themes/ultra/.
If the multi-site license interests you, we don’t mind subtracting the amount already spent.
Please, let me know if you have any follow-up questions.