This design of this 20 francs is known by the name of his engraver: Pierre Louise Aristide Turin (1891-1968). Turin was one of France’s premiere coin engravers during the 20’s and 30’s, when he also designed other coins and medals. The “20 francs Turin” were issued for circulation from 1929 to 1939. In addition to circulation coins, several proof 20 francs in silver or in cupronickel were minted during these years.
This coin is extremely rare in such a high grade. Its quality makes it very interesting for the collectors specialized in 20th Century French coins. However its price may be too high to attract other kind of collectors. PCGS graded 5 specimens of 20 francs Turin as MS64 and another 5 in higher grade, which are all proof coins. A price reference can be this one, which was hammered for 12.000 CHF in 2014, being considered the most beautiful coin of its type. Proof coins are significantly cheaper; as examples from the last few months, this one in silver SP67 was sold for $3.800 while this one in cupronikel was sold for 1.000 euros. As you can see, the price of the coin in auction is very difficult to estimate since it is extremely rare and its market is very reduced. Taking into account that this other coin -which is at least as rare as 1939 one- was not sold for 4.000 euros and that its market may be reduced to French coin collectors, I would think it twice before bidding more than 6.000 euros for the coin in auction.