Depends on how you define easy. It can be done in a few hours with a Tapco parts kit and a drill (to remove spot welds), plus a pistol grip and lug. However, because you are drilling through welds, it's not a drop-in conversion, and not one that's reversible if you decide to back out.
The good news is that the holes for the standard trigger group and pistol grip are already in the receiver. The bad news is that you have to drill through some spot welds and deal with spring-loaded parts to perform the conversion. Also the bolt hold open will require some modification if you wish to still use it.
The option I went with was just buying the skeleton stock (that has a pistol grip) and being done with it. My Saiga is a perfectly reliable rifle as it is, with well-made parts, and I like it like the way it is. I decided the risks and drawbacks to conversion were just not worth it.
I also enjoy the fact that many people will underestimate it, not knowing what it truly is.