if you are just messing around shooting at squash youre going to find brennees an expensive proposition.
buy a few boxes of brennekes, use up one box to note how they function in your shotgun and differ in POI from regular cheap-o™ slugs, and keep the rest for use on game.
if you want 2 3/4" slugs to plink around with buy a box of the Winchester SuperX slugs, they are cheap and effective and reasonably accurate foster slugs with manageable recoil. walmart has big econo-boxes of them pretty cheap, and theyre even on sale quite often.