Rob,
'Target grade' aperture sights are uniformly scalping in price
As most are produced in Europe, they have suffered a huge price increase due to the collapse of the pound vs euro exchange rate
The sight I use - the Gehmann Compact 590 is now ca. £145
Best bet is to look on places such as evilbay for second hand ones - the Anschutz sights are very good and seem to have the most availability.
A lot of chappies use the Williams aperture sights, generally obtained from :
https://www.evilbay.co.uk/itm/Willia...wAAOSwA4dWJF6m
Please subtitute real name of site
Have fun & a good weekend
Best regards
Russ