Searching around my stock for something nice, and thinking that Durer was great!
Here I come across issue from Czechoslovakia (dead country collectors can be interested), year of issue 6 July, 1968. 42 years ago, and so beautiful production, so quality of printing, engraved, color composition hardly that You can imagine it!
This issue is named after 37th Congress FIP, issued in block of four with gutter between two horizontally stamp. On gutter printed World Stamp Exhibition - that was held in Prague (today Czech republic capital city), topic is like You see, Art, Painting, Bible, and some more if You want. In Czech catalog (Specializovana Prirucka, edition from 1988) this issue is named also like auto portrait of Durer. What this Czech catalog have when talking about prices? Not something big, just 60 point - if it is not clear for collectors, it is quality point measurement accepted by Commission in any International held exhibition. Now, when I see on Michel (2007 edition) catalog, there is very nice prices for sheet of 4, 30.00 euro in mint condition, that will fit nice in any collection. But - probably, to find it in perfect condition will be little bit hard task, because period (42 year old item), glue that are cube shaped and very "soft", humidity will attack it "on spot" - because that, handle it very carefully when in Your hand!
Scott catalog (#1555) have prices just for single stamp, and mentioning that existed sheets of 2x2 with label, without stating prices, single stamp have it 3.75 $ against 5.00 euro in Michel, I think that this stamp deserve more than 3.75 $, near full prices of Michel, but it is upon collectors to decide.
I will see just according quantity printed, single stamp are printed 632 400 pcs, and sheet of 4 in just 27 431! Quantity is reasonable for this kind of issue, because many people will search for it if want to complete any serious collection of Art!
Now, we all know, that catalog prices are just "orientation" for market, and Michel catalog have it almost for any country reduced - and for Czechoslovakia, probably You will find it for minimum/maximum 50% catalog value - mean - very affordable for "People Who Know what Philately Is"!