Best sight for my saiga 7.62 still use irons? Cheapest rifle caliber to shoot besides .22lr?

The factory scope mount on the side of your saiga is the best option for mounting optics in my opinion, and there are many options available to slide right on that thing. The military surplus scopes for sniper rifles all the way to rocket launcher fit the same way and they come off and on with almost none if any loss of "zero". POSP scopes can be had for around 100 to 200 dollars and there are a few different magnifications. As far as cheap ammo goes, a saiga in 5.45 is around 400 shipped, shoots ammo that can be had for around 15 cents a round, where 5.56 or .223 is 35 to 40. Yes the cheap 545 is corrosive but cleaning the rifle should be part of owning the thing and taking care of your tools like a man! 17hmr is 15bucks for 50 average price and that is comparable to 22 mag in price and performance. All my humble opinion, I hope it helps.