A lot actually. You really don't need to get anything fancy to brest feed. A few nursing tops, two, maybe three nursing bras, some of those little "pads" in-case you start to leak, and a boppy! Which, if you play your cards right, you can either get at the hospital (they usually give you lots of leak pads, lanolin, a few books, and blankets) Or ask for them at your baby shower.
A GOOD brest pump will cost a few hundred dollars, but they pay themselves off !!
A can of formula = approx 15 dollars at walmart.
1 can can last about 1 week.
So, you can do the math from there.
I saved a TON of money brest feeding!!! I didn't need all those fancy "nursing tops" I only had the tank top (which went under my shirts) and two nursing bras! And I did fine! But, if you are really trying to save money, boob is the way to go!!!
EDIT: A lactation consultant? You can find resources for all the breast feeding questions online, and most hospitals offer it for free!!! FOr millions of years women have been nursing, trust me, it saves you money! (and helps with weight loss!!!)