Getting to know the different eras of production would be an important first step in understanding Doxa divers. I’ve been studying them casually on and off for a few years, and by no means am I an expert. But there are a few observations I can share.
Septentrio’s excellent example you referenced is from the first few years of production by Doxa. That watch sold here on OF sometime back. Very appealing and authentically aged lume. Being of the early, first production typically carries more interest for collectors. Higher values here - and all hinges on condition and particular model (dial color).
The Synchron era is used to describe the watches from the early 1970’s when the Doxa brand was rolled up with several others as a result of the Quartz crisis. The watches were very similar to the earlier production, but have the Synchron logo visible on the dial in most cases, but not all. See that logo printed above the Doxa name in the image below. The three pointed symbol appears on either the caseback, crown and dial, along with tritium lume as identifiers. The text at the bottom of the dial indicates Tritium Lume, and < 25 micro curries of radiation as the laws of that era demanded. These typically have some reduction in price from the original first years of Doxa production described above.
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The more modern watches made currently are superb as well, and you can find a nice example on eBay or elsewhere. They have superluminova lume, and can light up a dark room. A Very neat and useable modern watch. I’ve seen these sell for approx $1750-2000 USD give or take. Sxl2004’s Divingstar example in the post above with its yellow dial and well paired strap is killer, and a fine way to have and enjoy a Doxa diver. I believe a pre-owned but worn example of a watch of this era can be found for less with patience.
a bit of research will give you some price points to work from. There are quite a few out there for sale among all of these three broadly defined categories. I believe with some study and patience you may be able to find a watch at a price you can be comfortable with.