Another plug for cloth nappies - I'd hate the thought of having to buy new nappies all the time, we'd never afford it! Just chuck them in the washing machine every couple of days. It's more expensive at the start though.
Otherwise, though, I'd say about 8-10 a day for a few months.
Asda have thing that if you sign up will get a voucher and get a free packet of huggie nappies and couple other things. Possibly a few other deals like that about. I'm using resusables so haven't investigated.
I'd get all the free ones you can for the first few weeks until the poo settles down then use washables - it's not that much extra laundry but it is MUCH cheaper - especially if you're thinking of having more than one DC. I get most of my disposables second hand off either ebay or usednappies.co.uk. Once they arrive I give them a wash in my washing soap so I know they're washed in non-bio and then that is it!
8-12 nappies a day until a little older. Once 6+ months I found 6 a day was all we used. Definately going reusable this time here! You can use muslins with a wrap on for newborns, which I'm going to try.
I find Asda do v good deals on the big brands like Pampers. Also I used cheap own brand nappies during the day when DS was needing changed frequently (first few months) and used the more expensive (but more absorbant I find) for night time.