What previous posts said - babies don't need much! However, you may need to factor in the cost of childcare.
We hardly felt - financially speaking - the arrival of DS, as nappies etc can be bought cheaply, and I breastfed.
You can spend as much or as little as you like on everything else. For example, we could have easily spent £££ on nursery furniture but didn't - we got an ikea changing table for £25, an ikea cot for £55 and one of the more expensive ikea mattresses for £70 or so. You can also buy a cot for £500, or get one of gumtree/eBay for £10.
The most expensive thing is probably the pram and the car seat but there are deals all year around, we got ours from the mamas and papas August sales and the pram & infant car seat were £375, sold as a set. Baby clothes are not expensive and you can always stock up in the sales.
We put our son in nursery now that he's 1, two days a week and that costs us £50 per day, at the expensive end for where we are but not as expensive as the South. We are not eligible for any tax credits/childcare element of tax credits but lots of people are - the money saving expert website has really good info on this.
So, I'd say, if you can save, great, if not, your costs will probably only go up when /if your child starts nursery.
Oh, and - it's very easy to spend money on maternity leave (coffees, baby classes, swimming lessons - some of the stuff I did cost £5-10 per session so it adds up) but there are so many free baby groups, stay and play sessions etc, especially if you live near a good sure start centre.