Shotgun sights
If you want the cheapest route I used a Williams peep sight on the rear and a generic rifle ramp soldered onto the front wit a high brass bead sight.
This was effective and relatively inexpensive although the drawback to the williams rear peep is there is no protection. It is a very low profile unit though.
This setup definitely isn't high up there on Tactical Cool points either if that matters to you.
I have used the Wilson setup and it is state of the art although neither end is protected and although the units are very sturdy they are out there on their own. Expensive too.
I have a Mossberg 590 and I have to say the Mossberg ghost ring sights are excellent. They are very well protected, sturdy, and very high visibility and user friendly.
I bought a set and am in the process of mounting them on a 870 tactical gun.
Something else to consider.......
After having used many different adjustable sighted combat and hunting shotguns there is a lot to be said for a plain beaded barrel.
It is a little dependant on the particular setup as all gun/barrel combos don't shoot exactly to point of aim but when they do and or you are familiar with the particular gun they are pretty damn effective!
I have a 14in 870 with a plain barrel with a extra large brass bead and this dman gun will put generic foster slugs all on a paper plate @ 50yds on point of aim as well as throw shot in the similar point of aim.
Goes without saying it is a keeper!