Honestly coming up with an idea of how much a baby will cost for you is very hard as it is different for everyone. It depends on the brands you prefer and some of the choices you will make as parents. For example, do you plan to use cloth or disposable nappies? Do you plan to breast or formula feed? Do you want to buy all new clothes for your baby or do you not mind buying used clothes? How much are your families willing to help you out as far as purchasing items for baby goes? These four things alone will determine your baby budget greatly.
Also, the amount of nappies you use daily will change as your baby gets older. I would say that most newborns probably use anywhere between 9 and 12 nappies a day on average, but my 9 month old uses about 5 to 7 nappies a day.
Newborns also nurse or take a bottle every hour or two (if you plan to bottle feed the amount of formula you use for each of these feedings will depend on how old your baby is and how much they personally feel like eating as some babies eat more or less than others. I don't have a whole lot of knowledge in the formula department as far as how many oz each age is likely to take as I breastfeed). My 9 month old however has been eating solids since 6 months and now only nurses about 5 times a day (give or take, it varies sometimes) because he eats a bowl of baby oatmeal in the mornings and 3 or 4 jars of baby food a day.
Speaking of baby food, you will need to think about whether you want to purchase pre-made baby food or make your own at home when your baby is old enough to be introduced to solids.
Our parents and grandparents helped with a lot of things, so we didn't have to make most of the big purchases ourselves. The big stuff is expensive, but can also be used with subsequent children and most of it is necessary and well worth the investment. By the big stuff I mean the swing, crib, crib mattress and bedding, stroller, exersaucer, pack and play, bouncer, car seat, dresser, ect. If money is no object then I recommend getting these things new. If you're on a tight budget though it's probably okay to get all of these things used except for the car seat as it's impossible for you to know if it has been in an accident or not and can be hard to figure out if it has expired (yes, car seats have expiration dates). This of course is providing that none of the things you get used are a model that has been recalled (do your research carefully before buying any of these things used). I would also recommend getting a convertible crib that will grow with your baby because even if you plan to co-sleep for a while co-sleeping may not work out as long or as well as you hoped (my son decided that he wanted to sleep by himself after 3 months). It will also provide a toddler bed that you then do not have to buy (unless you plan to have more children and have them within 4 years apart from each other). I also recommend making that convertible crib one that has a changing table attached to it. We have one and it's been incredibly convenient. It's great for extra storage space, doesn't take up much extra room, makes nappie changes quicker and easier, it isn't hard on our backs because we don't have to bend over to change DS, and it turns into a night stand or end table later.
If you plan to breastfeed I would recommend investing in a hand pump if you are staying home (if you are currently working and planning to go back to work or plan to start working after the baby gets here then I would recommend an electric pump and a pumping bra. They're pricey but well worth it). You can check and see if your hospital will provide you with a hand pump though as sometimes they do (they did for me). This of course is if you don't plan to do a home birth.
If you plan to use cloth nappies you will need at least 25 cloth nappies for a newborn. I would use prefolds for newborns as they fit them better. Save the one size cloth nappies for when baby outgrows the prefolds (basically when they hit about 8-12 lbs if you don't end up with a big baby or if your baby doesn't put on weight very quickly. As a newborn my DS was small but put on weight very quickly and that weight gain evened out as soon as he was caught up to where he should be for his age). Great sites for inexpensive and well made cloth nappies are
www.kerrbearkids.com and
www.lovelypocketdiapers.com. 25 cloth nappies is also if you can do laundry every 2 days. It never hurts to have as many cloth nappies in your stash as possible though. You can probably get away with spending about $300-$500 roughly on a cloth diapers stash, but in the long run it will save you money and you can reuse the same cloth diapers for subsequent children (if you don't plan to buy any more after your initial stash no matter what your children's genders end up being then I would stick to gender neutral prints and colors).
If you plan to use disposables, don't buy in bulk as the lady above posted. Buy wipes in bulk all you want, but stick to one big box at a time of whatever size nappie your baby is in at the moment at most or you'll end up with more nappies than you can use in that particular size as babies can grow out of a size very quickly, especially sizes N, 1, and 2.
So really you just need to do some research and decide what choices you want to make as far as your parenting style goes. Once you've decided what you want to do as a parent, then look at products that comply with your wants and needs and figure out which prices work for you for the quality. Then add up the costs of those items and viola. You have a rough estimate of your baby budget. You should also always at least slightly over estimate how much money you will need to have saved up to ensure that you will indeed have enough. Microsoft Excel spreadsheets can be very helpful in planning a budget.
I hope that I was able to help. Good luck with your WTT baby budget and financial goals for reaching that amount.