Farstrup 210  

I've just found two superb chairs in a local second hand furniture store - these chairs are model no.210 from the danish producer Farstrup. The chairs are very comfortable and the design is lovely. The seats are in black vinyl. On the bottom they are stamped 'Made in Denmark by Farstrup / no.210', quite like in the attached photos found on the web (no other mark/label is attached). From what the store owner told me, they come from Switzerland.
Now, based on that stamp, can you guess the decade? 50s,60s,70s?
What's their fair price (not in mint condition)?
Tx.
PS: I paid 9 eur / piece.
<img class="wpforo-default-image-attachment wpforoimg" src=" http://old.designaddict.com/sites/default/files/fo