This is a topic that has interested me for a long time. I do not know why some older fragrances keep their retail price, while others decline. It may simply be continuing demand, as you suggest. It may also be whether the manufacturer keeps its supply chain tightly controlled: Estee Lauder/Aramis and Guerlain both continue to charge relatively high prices for older fragrances. (And I would argue that they are both worth it.)
Anyway, there are many older, historically significant fragrances that you can sample quite cheaply. As a sort of tour of the development of men's fragrance, I would suggest:
- 4711: One example of the original eau de cologne concept.
- Pinaud Bay Rum: A perfect example of the bay rum type of scent.
- Dana Canoe: An excellent fougere in the old-fashioned style. (And incidentally, the only fragrance that Dana seems to be producing with any acceptable quality these days.)
- Guerlain Shalimar: One of the few Guerlains that can be found cheaply, and still a masterpiece. This one is not a men's fragrance, but it is beautiful and some men enjoy wearing it.
- Some representative examples of the heady 1970s: Halston Z-14, Lagerfeld Classic, Royal Copenhagen, Grey Flannel.
If you can visit a JR's Outlet, you can find many fragrances for $10 or less, including some obscure classics. Perfumania is also your friend. Have fun exploring.