Satch
Hall of Fame
Right, those are very old racquets that are not even sold anymore and those prices are from a long time ago. Those racquets originally sold for a lot more when they first came out and were in regular production. Once they were discontinued, the prices dropped just like discontinued racquets today are cheaper than a newly released one. For example, this racquet was much more expensive than $69.99 when it first came out like 8 years ago: http://www.tennis-warehouse.com/descpageRCPRINCE-TTW.html
(BTW, "discontinued" means it's no longer being actively marketed as a new model although they can continue to manufacture it.)
The Head Prestige Tour was very expensive back in the mid-90's. Your links show prices from 2002 when none of those were new racquets anymore.
no discontinued means no longer manufacturing. Those model were some old models left in stock, or some reissued ones.
Anyway it doesn't matter it just prove my theory that it's not material oil or something else -it's marketing, they were selling that rackets so cheap because they were no longer main models, but they worth exactly the same to produce.