Yeah that sucks. If it turns out that support can’t set you up with a decent upgrade pricing I can tell you that their Waves Upgrade Plan (WUP) does go on a 25% off sale several times a year. So that is something you can look out for.
The other thing would be Horizon going on sale cheaper than what it would normally cost you to upgrade. Or even the bundle up that would include all of Horizon’s plugins plus extra. It’s always a good idea to keep an eye on sales if you’re planning to upgrade your plugins.