Hello jgourd and welcome to the forum.
Do you mean the "149.99 excl. VAT" price?
If so, then that is the introductory price for Upgrades from previous versions of AmpliTube AND for crossgrades from a Qualifying Product (an iK Multimedia product with a regular list price of 99.99 or more (again ex VAT)). I would think that you have a Qualifying Product.
If you log in to your User Account and go to your User Area: Crossgrades/Upgrades you will see what is available and the prices that are relevant to your particular ownership of product licences.
https://www.ikmultimedia.com/userarea/eligibility/NB: The introductory prices end at the end of the year (tomorrow). And, before you ask, there is no publicly-available information about crossgrade / upgrade prices after that. Personally, I would not expect them to be better.