dude,

an 8X8 inch could probably go for about 7g-14g of bud, depending on how high you feel like getting! My friend made the sickest brownies once, but she didn't use the bud-butter method. She just ground it up to a fine dust and mixed it into the batter. If you wanna save on using the good stuff, use some shwag or the leaves as a PART substitue, not for the whole thing.
good luck!