You can borrow my gently used babies for a few years to see if it's something you want to go ahead and do lol. I don't know why you specified "daddies" since there are plenty of mommies here as well so I'm just going to butt in and answer.
A lot of my dollar amounts will depend on how frugal or expensive your tastes are, how much insurance you have, how much your family tends to spend on you for gifts, etc.
I think it would be fun to have a surprise baby, but I've planned all of mine. I'm way too controlling. I do NOT want a December baby, and we also purchase AFLAC two months before trying to get pregnant, because you can profit a couple thousand dollars from it, but you have to have it BEFORE you get pg. But you wouldn't want to get it if you weren't officially trying, because you'll just waste a lot of money on premiums if it takes a long time to get pg.
The first expense to think of is how will you pay the bill? If you have insurance w/ maternity coverage (most do not unless through an employer), then be sure to know what your ded. and co-insurance is, and start saving for that now. You can expect the hospital bill to be around $7-10K, for a normal routine delivery w/ no complications. If the insurance is through an employer, think of how likely you are to still be employed with them at the time you may get pg. If it's through her employer, keep in mind she may not continue working.
Next expense will be maternity clothes. If she is very tall/thin, she may not have to get as many as the average person, and again depending on how pricey your tastes are, I would plan at least a couple hundred dollars for maternity clothes.
The next thing that may change is your income. If you need both incomes to be ok, you may want to consider that some women get so sick that they can not work in the first trimester. She may lose a lot of income to be staying in bed resting. Many women also get put on bed rest if there is a complication. And then most women don't want to work the last month or two because it's pretty much too uncomfortable to move let alone work. Although some want to work until the very last minute. So be prepared to lose her income.
Personally, I felt it was important to take the last 2 months off, and stop working then, because I knew I would never be alone the rest of my life, it would never again be just me or just us, and I wanted to catch up on some projects, have a lot of time to myself for leisure, and be very well rested. I think it really helped me to handle the transition a lot better, but some women would go crazy not having anything to do.
And then for the baby stuff--again, depends on your tastes and how many gifts you'll receive, but I'd say plan on about $5K for baby stuff. It's only really expensive w/ the first one, the rest are a lot easier because the big ticket items are already purchased. But generally you'll want a crib, cradle/bassinet, stroller, car seat, dresser/changing table, rocking chair/glider, a few things like a swing or bouncy seat, some toys etc.
You'll go through a LOT of clothes the first year because they change sizes every couple of months. I'd say plan on about $30-100 for clothes for each of the sizes Newborn, 0-3 months, 3-6, 6-9, 12-18, 18-24. So to get through the first 2 years you probably need about a total of $200-500 for clothes. And maybe another $30 for about 2 pairs of shoes in the older sizes. Once they get to 2 years, the clothes usually last longer, but if you have big climate changes in your area then you'll need summer clothes/winter clothes and shoes. The clothes start getting more expensive when they are older though, so plan on about $200 a season plus about $40-50 for shoes. Keep in mind that I'm pretty frugal so I'm coming from Target/Sears price ranges.
She may plan to breastfeed and do just fine, she may not be planning on it, or plan on it but it not work out. If the baby ends up on formula, plan on about $100 a month for the first 6-8 months, and then it lowers from there as they start eating solid foods. I'd guess that most people spend maybe about $30 a month at the most for solid foods. I never buy baby food though, I just mush up whatever we are eating for dinner already.
As far as any other expenses down the road, depending on your insurance situation, it's probably around $200-500 to go from a couple's insurance to a family insurance. You'll also want to make sure you have good life insurance. Your other expenses will be things like if the baby has any medical issues you could have bills for that, and then they are always needing clothes and shoes, you will need an infant car seat and a convertible car seat, and then later on a booster seat. (My kids will be in a 5 point harness until they outgrow them around 7-8 years old, so their car seats need to be good quality ones that will last.) You may also have expenses starting around age 3 for activities if you choose, things like soccer or dance, etc. and at age 3 is generally when you have to start paying to get them into places.
That's all I can think of for now. Good luck!
Oh-ETA: Forgot about diapers. Plan on about $40-60 a month for diapers. You can cloth diaper which will be a LOT more upfront and then less in the end. I potty train my kids starting before they turn 2, seems like most wait until closer to 3 but I'd rather save a year of diaper costs!