Rare 1926 Block Scott's # 344 ( Help )

Starting to go throught my stamps , and came across these beauties. Hoping I can get info and value about this block. So this is were I'm at with info that they made only 1000 .Russia 1926 green 3py6 . And this block is really rare. but in this condition even rarer.

Rare? SG (2010) values this at £2.50 for a single. Or am I missing something?

A auction last year this block with sold with a fold and descoloration on glue sold for $325 . ebay which I don't trust is selling for $150 used for a single stamp.And other auction like decamper ect for around the same crazy prices. I don't have a current price guide, so that is why I am confused ? I figure I will get staight answer from members here. but also what the details are about this bock for my knowledge

Here is some more info on block. They are a dark green in color . also I don't know if it matters I read that there are 2 color back glue paper white or cream. This seems to b in the middle ? Cream ?