First, I do not now buy many plans. I build from kits, short kits, self designs, and sometimes combining stuff from crashes. I like to just do things different than the typical ARF.
I do have a significant number of Old Timer and kit plans. I have the last catalog, I think, that the late John Pond published, 1999-2000 combined for all disciplines. John Pond was a fantastic person, and he maintained the most abundant amount of existing model airplane history in his fantastic collection, which is now in the hands of AMA.

Looking through that catalog and some of AMA's pricings for such plans, AMA's prices are right in line with the catalog, of 9 years ago.

I did not check the plans from AMA's MA magazine.

I am currently doing several old kits for a renewed interest in Old Time CL Stunt.
Ringmaster, one S-1 flying, an F and B Viking for a Super Cyclone on spark, almost ready to go and a Veco Classic Thunderbird 2, just started, one of which I won many trophies with, back in the early '60s. (Off topic, they won't allow the modifications I made back then to make that machine a First Class Stunt Machine.)
So back to topic, I am familiar with old plans and prices and I see no big problem there, with AMA.

Mongo offered a fair statement which I suggest may have a very profound effect on the plans business.