Patterning your shotgun comes as the single most important thing to be done after finding a gun the feels and fits or have it fitted.
Shotguns like rifles can be tempermental about what gives the best performance out of a particular gun/choke combination.
While there are plenty of aftermaket chokes only resort to them after seeing that the ones that came with your shootgun don't preform to your expectations.
There is no such thing as "cheap " shotgun ammunition. In that last 10 years or so thanks to sporting clays popularity there's never been such a selection of ammo. But the public continues to be hosed by some manufactuers. Prices doesn't always equal quality. The Patterning Board is the great equalizer in shotgunning.