I saw this pop up a couple of hours ago.
About the price, it is only a concern to Avast Software and for the users really interested in the offer, and the offer can change from time to time. For this topic, that is OT.
The really important thing (in the context of this specific forum's topic) is if this type of "warning" is going to be "too frequent", or "annoying".
After years of using Avast, this is the first time I've ever seen such a "warning", so it doesn't bother me. I think it is a legitimate way of offering discounts to potential buyers. As I said, it depends on the frequency.
Although I don't think there is a GUI method to avoid it, I guess that a complete silent mode would block it. I personally don't use silent mode, and I won't use it for the only purpose of blocking this notification.
In addition, as with other pop ups, it is still possible to change the time it is going to be displayed. I personally won't change the displayed time, unless it turns to be "too frequent". I think that, during the years, Avast has been both respectful and useful to the user, so I don't believe it is going to be "too frequent".