Avent bottles are probably the best out there, hopefully your wife breast feeds over formula, that's where it really gets expensive. breast milk can be stocked up and frozen, later thawed with hot water running over it or placed in a cup or glass of hot water...always check the temp before giving it to the kid. Diapers are the next expensive item, you'll just have to figure out which works best for you. most things you'll need will come during the baby shower if your wife hasn't already done that.
I'm no expert, just experienced from my three kids, now 18,13, and 11 yrs old. good luck and best wishes to you and yours.