The frame to me looks very Italian. In fact, I can't recall any French made frames that used those lugs. It doesn't look like a constructeur level of work; it's more likely to have come from of a mid volume maker. And, with a 70mm Italian threaded shell, chances if being French are slim to
nul.
There were some Italian companies (including CBT Italia and Tecnotelai) that built a fair number of frames for the French market, but this frame doesn't look like it came from either of those shops.
Also, while anything is possible, I'd be inclined to think it's not a Viner, either. I've never seen those kinds of stampings on Viner BBs. Granted, since the frame's been repainted, those could have been made before the paint was applied.
When it comes to the lugs with those curly cutouts (I guess this is gonna be more of a reference post than for ID of this particular frame), they were not uncommon on Italian bikes, but not nearly as popular as the Italian Prugnat S4 knockoffs (
which may have been made by Agrati, at least according to Boeris).
I'm not certain who manufactured these lugs but they appear to have come in at least 3 variations:
If you look at some Gentleman and Super Gentleman Olmos of mid to late 70s, you'll find the same cutouts but with plain sides - no side cutouts (
Style #1):
If you look at late 70s Guerciottis of roughly the same period, you'll see the same 'curly' cutouts, but with Prugnat 62/S/D-esque 'hooks' on the side (
Style #2).
Finally, on some Viners (relatively few) you'll see those cutouts with small triangular cutouts on the side, like on the mystery frame here (
Style #3). Viner employed Style #1 more commonly than #3.
These lugs (in the three variations) show up somewhat at least somewhat regularly on frames from these marques:
Leri - Style #1
Viner - Style #1 (more common) and Style #3 (less common)
Olmo - Style #1
Bottecchia - Style #1
Rossignoli - Style #1 (might be contract builds by someone else)
Elios - Style #1 (might be contract builds by someone else)
BMZ (this includes a lot of brands they built for, like Lazzaretti, Performance, Palo Alto etc.) - Style #1
Guerciotti - Style #2
Lino Tempesta - Style #2
Renesto - Style #2
Aquila - Style #3
Freschi - Style #3
Style #3 is more commonly found on Aquila and Freschi frames than on Viners:
I'm not claiming the mystery frame here is either Aquila or Freschi (the frame isn't fancy enough for a Freschi and I don't think Freschi built any frames without fast back stays, did he?), just trying to show that these lugs aren't exclusive to one frame maker.
It might help the ID efforts to get a few more closeup pictures of:
Full rear dropouts (with both seat and chain stay ends visible)
Full front dropouts (with ends visible)
Side of the seat lug (with the full seat stay cap visible)
Brake bridge (including any reinforcement tangs, if any)
The entry/exit points for the internal cable routing on the top tube
As for the value, I too have a hard time seeing this go for more than $500, considering it's an unknown frame with Shimano 600 drivetrain.