Small correction.
That sight is not a Diana 100 sight, it is a Gehmann sight. A model 590 L.
The sight alone retails for 180 to 200 dollars sans the adjustable iris mounted on it.
The diopter looks like it has polarization adjustment and possibly diopter correction as well. You are looking at close to 500 dollars US for the rear sight set up.
gehmann.com
Retail price of the sight
Gehmann compact rear sight now available at Oberle Enterprises. Give us a call for all your Competitive shooting supply needs. 720-670-6818
oberleenterprises.com
Found the diopter as well
Incorporates the 550 irisIris adjustable over a wide range of 0.5 - 3.0mmTwo separately adjustable polarisation filters:Our Gehmann polarization filters offer two key advantages that lead to noticeably better and longer-lasting performance of t…
gehmann.com
Retails for close to 300 USD.