Ours just turned two.
Best investment ever was buying an electric breast pump for the wife. She got herself on a cow-like milking routine and we were able to start putting breast milk in the freezer in the garage. After about six months we started feeding him from cold storage. So basically were able to go over a year on breast-milk for less than six months of breast-feeding. Never had to buy formula.
Next, Sam's Club is your friend. The Sam's Club Member's Mark diapers are 11 cents per diaper. I couldn't find a cheaper one anywhere. They aren't like normal store-brand diapers. They work. Once we switched to them we didn't have another blowout. (Blowouts suck).
Doctor visits suck. My insurance covered well-baby visits, but capped immunizations at $1000. Well shoot, they bust through that $1000 in no time! Started taking him to the county health clinic and getting those shots for free.
Don't let your wife go nuts decorating a nursery for a baby who has no idea, and doesn't CARE what is on his/her walls!!! I bought a nice safe crib. That's it. No frilly curtains. No light blue paint. Nada.
If he/she sleeps in your bedroom in a bassinet for the first few weeks at home, make sure he/she takes NAPS in the crib. It will be a thousand times easier to transition them to a crib if they're already familiar with it.
As for clothes. Stay away from anything you might find at a mall. Put a lock on the wife's credit cards. Baby clothes are a massive ripoff.
If my wife can't find what she needs at a thrift-store or consignment shop I give her permission to go to Walmart or Target. Fortuneately she is just as cheap as I am!!!
If you are a two salary family (I was), don't necessarily believe the wife when she says she'll go back to work when the baby was born. My wife changed her mind. It takes a lot of rebudgeting to go back to one salary at the last minute.
BUT, if she does go back to work, factor in daycare plus gas to and from daycare etc. It's not by any means cheap.
Those first 3 months are a living nightmare with the baby. Up and eating/pooping every 3 hours. It's horrible. Cowboy up and offer to watch the baby and tell your wife to go out, see a movie, go shopping, go to Starbucks...something to get her out of the house. Her sanity will depend on it.
Full disclosure: We don't live anywhere even CLOSE to our nearest family members, so we haven't had any help or free babysitting.
Good luck. It is a horrible, awful, life-changing event. Nothing will ever be the same... but... a few times a day he comes over, climbs into my lap, wraps his arms around my neck, gives me a kiss on the cheek and says, "Luv Daddy".
Then it's worth it...