I was looking through some early White Dwarfs this morning and in the back were adverts and price listings for many UK resellers of the time.
D&D Basic Rules, Dice, Adventure.......... £8.95
D&D Expert Rules, Adventure................ £8.95
Module
B2............................................. £3.50
AD&D Dungeon Masters Guide............... £9.95
AD&D Platers Handbook........................ £8.95
Module
C1............................................. £4.50
Module
D1-2.......................................... £4.50
Dragon Magazine.................................. £2.50
I could be looking at a seller's BIN list on eBay.
The majority of xD&D stuff still sells at about those prices today on eBay.
Given the inflation over the past 20 odd years, the majority of this stuff must have depreciated dramatically.