Drevet isn't a name you see often, but from what I recall, it's a good one. I had a Drevet gun, very nice sideplated boxlock 16.
Your photos are indeed fuzzy. If you can get better ones, we may be able to tell you more. But here's what I can tell you so far:
The PT and PM mean the gun was proofed with two smokeless powders: T and M. Proof with M stopped in 1914. Combine that with the Grand Prix (grand prize) 1900, and you've got a gun made between 1900-1914. And that's pretty good on a French gun, because they don't use date codes.
"Non pour la balle" means "not for ball". Not a slug gun, in other words. Not sure when they stopped using that mark. "Modele depose" simply means the name was registered with the French government. "Canon plume" is an expression for a very light barrel. "Plume" means feather. Note your gun has almost no rib. That's the "plume" part. I can't make out the "canon de" part, but your "durpis" is wrong. "Garantie" simply means guaranteed.
Interesting gun. Looks like almost no engraving on the sides of the receivers, yet a fancy, scalloped back where it meets the stock, and really nice work on the fences (the leaf engraving).
Really tough to put a value on it. We'd need better pictures and more information. Such as, condition of the bores (bright and shiny, badly pitted, or somewhere in between), whether it locks up tight (take off the forend, grab it by the muzzle, and move it back and forth rapidly with a sweeping motion. If you detect looseness where the barrels join the receiver, that's bad. How bad depends on how loose.) Also condition of the wood. Any chips, cracks, or significant dents? Checkering still sharp or all worn?
It was certainly an above average gun when new, and the French didn't make much junk. (St. Etienne is where it--and most French guns--was built.)
Have a gunsmith or someone who knows doubles well look it over before you shoot it. It should be safe with "modern" ammo, but it's likely very light and would probably kick like heck with most factory American ammo. Light shells (2 1/2"--it will certainly have short chambers unless they were lengthened somewhere along the line) from either RST or Polywad would be the way to go. Good luck, and if you can post better photos, please do so.
