My rationale is it's a shotgun that randomly spews lead of any brand whether the ammo's expensive or not.
The trick is finding the brand that it spews the best.
While shot is always random, all different brand shells pattern differently in each shotgun barrel and each different choke. Since you have a fixed cyl bore barrel half of the equation is already solved for you. Some may shoot better patterns with the cheap stuff, who knows that's why you always here about people "patterning" their shotgun for particular loads. It will probably shoot them all different. If cost is a concern and you don't necessarily have to have the tightest patterns go buy several different brands of cheap stuff and have some fun seeing which one it holds the tightest pattern with. Then buy a bunch of that kind.
Don't count out the reduced recoil shells if your trying to get a good tight patterns and are not worried about maximum penetration. They are lower velocity and lower pellet count but sometimes they do pattern really good.
Just to add because it's that time of year, one of my favorite targets for patterning is Christmas paper. Take some left over or cheap dollar tree type and turn it around backwards and put a few aiming dots or cross hairs on the white side a pretty good distance apart with a sharpie or just a can of black spray paint. Tack up one end and roll it out in between some fence polls/ fence line, tree's, two target stands or whatever. If you have a pretty steep shooting berm around that can work OK to just keep the angle in mind.
I think this is cheap and saves alot of time by not having to shoot, rehang, shoot, rehang. Shoot one round at each dot with one type of ammo. Go mark each pellet hole somehow, straight mark to the right, circle, triangle, box, whatever just mark them all the same per brand. Next round change ammo and mark. Continue until out of ammo or paper is starting to get too damaged to read and mark the holes good.
Merry Christmas,
HUB