The brewer's yeast in supermarkets is a cooking ingredient. I wouldn't try making beer with it.
Good yeast is fairly inexpensive, and it has such a monumental impact on your beer, that I you don't want to shortchange yourself.
Oh don't give me none more of that Old Janx Spirit
No, don't you give me none more of that Old Janx Spirit
For my head will fly, my tongue will lie, my eyes will fry and I may die
Won't you pour me one more of that sinful Old Janx Spirit