Hi, Mike, I'll second Vic's advice, but also offer some additional info.
No, not all manufacturers are out of business, though there are many. The first commerically-viable flat figures emerged in the 18th century, and some makers ("editors", they're sometimes called) are still in business, others have come and gone.
Opinions about the quality of any given figure may vary. You have to look at the quality of the engraving and casting, then take into account the quality of the painting. Some flats are very nicely detailed, but they were farmed out to cottage-industry painters whose skill varied wildly from one painter to the next.
Along with checking out the British Flat Figure Society, may I recommend to you the Berliner Zinnfiguren site:
www.zinnfigur.com The site and store are run by Hans-Günther Scholtz, whose father, Werner Scholtz, established his own line of molds and a catalog. BZ carries the Scholtz line, as well as others, some newer, some older from older molds. Many figures are available either painted or as unpainted castings. They also have an extensive "flea market" area of figured from old collections. I recommend browsing their site, and even subscribing to their hard-copy catalogs. That can give you an idea of what current prices are, for new figures and for second-hand figures.
Also, another maker of flat figures, albeit in 54mm, rather than the traditional smaller scales, is Conrad Schulte, whose online shop is at
www.fredericus-rex.de. Conny also maintains the online forum HZ-Forum, which is in German, but has a lot of members who work almost exclusively in flats--it is the German "national format", after all--and you might find it interesting to browse both the shop and the forum.
Hope that all helps, prost!
Brad