Alanint has it all correrct. The original autos just had the markings changed and a few internal parts swapped out. I've handled a couple. They are extremely rare and would run in at least the $40K to $50K range right now, I believe. A standard 1921 Colt, by comparison, would typically go for a minimum of $25K to around 40 - 45. Wartime AOC or Savage Thompsons are $18K to maybe $26K.
The current semis from Kahr would sell for $700 to $800 used; new around $1500. Quality can in no way be compared to the real ones, but they look sorta the same...except side by side. They are fun guns when they work. And Paul Krogh of Delta, Colorado, can turn one into a functional and reliable work of art...just beautiful...for a reasonable price. But you may have to wait up to two years. For a guy who is serious about his Thompson, and lives in a state where full auto is impossible, "PK" and his 1927A1 rehab magic is the only way to go. Sorry, there is no website. Word of mouth is all this craftsman needs.
All the guns marked 1927A1, etc., are the recent Kahr flavor, although a few may have been made by Numrichs earlier. All of them are marked "Auto Ordnance", although the real company has not been around for over 60 years. The late George Numrich just began using the trademark around the 1960s; nobody objected because the original company and most of its people were dead; he later registered it in New York; his partner/successor Ira Trast sold it to Kahr; their lawyers misunderstand and think there was a "succession" of the direct AOC lineage, and Kahr ads pontificate about the unbroken tradition and heritage, etc. Some self proclaimed "authorities" in Thompson land, one or two in particular, also misunderstand and argue vehemently, but never have any luck supporting their bogus "unbroken succession" claims with documentation, beyond what they make up from whole cloth and hot air. The perpetual debate is interesting, and many thousands of words have been written and argued about it. It may fatten the bank accounts of generations of lawyers, and will certainly entertain generations of gray haired Thompson collectors with nothing better to argue about.
Thank heaven, we have few such uncertainties about Lugers, since the Germans documented everything to death and little was left to chance.