The best way to know the current market value of Art Deco armchairs is to check eBay*.
The best art deco furniture was made in France, for it was in France that Art Deco took off with the 1925 Paris Exhibition.
And within the Art Deco, there are two main currents:
(source: "Art Deco", Libriitalia s.r.l., Le Perle, I Libri per Tutti, 2002)
Le Corbusier (1887 - 1965)
This a very famous Le Corbusier arm chair designed in 1928 (here an item made in 1975 in superb conditions).
Actually this was called "siège grand confort" and was designed in conjunction with Charlotte Perriand in 1928. Other pieces included the famous "siège à dossier basculant" (a re-interpreation of the usual colonial chair) and models of "siège tournant". The basic idea was to substitute wood with metal and leather.
Le Corbusier real name was
For Le Corbusier there were two types of furniture : movable and storage.
"A new term has replaced the old word furniture, which stood for fossilizing traditions and limited utilisation. The new term is equipment"
Le Corbusier-Perriand design (1928) - arm chair made in 1975. source (Originally it was named "siège grand confort", grand-comfort armchair)
And the even more famous "siège à dossier basculant", again a Le Corbusier-Charlotte Perriand cooperation.[source]. The first chair using steel tubes was made by Marcel Breuer in 1925. steel and glass were the new magiv materials the avantgardists designers rushed to employ in the late 1920s. The "metal furniture" was at his peak in 1928, a magic year with the invention of the above chairs in the "machine age" aesthetics.
Charlotte Perriand (1903 - 1999) was a pupil of Paul Follot et Maurice Dufrène, she became assistant of Le Corbusier in 1927 until 1937. She also worked with Leger, the artist.
A very talented designer, she was first refused superficially by Le Corbusier and then hired when he was shown her talent.
Further Reading at: designmuseum.org
* Ebay gives you the price not only today but NOW.
It's not important to know that that piece of furniture, or those art deco sofas, those art deco beds, art deco armchairs fetched so much 10 years ago. We live in the present and all professional antique and vintage dealers will tell you that the value goes up and down according the the demand not according old price catalogues.
Here is an article on the difference between antique and vintage.
Moreover, is there a way to know if in general the Art market (I think I can include also the antique market) is doing? Is there any special index? Yes, the artprice.com market index is considered a valuable asset for professional investors. And here it is: