I know this is of no practicle help, but you WILL cope. I found my maternity pay from work with all the goverment maternity pay suprisingly adequate....
I found our most expensive items were the buggy, cotbed and car seat. Once these are purchased, the rest is not all that expensive.
We also did things like if there was a buy one get one free on babywipes, we'd always buy lots even before we had the baby, same with nappies and other baby items.
It will be harder financially but that's just the way it is....if you have any outstanding debts now is the time to try and clear them. Also, suggest to your DP that you start looking for good second hand items.
Caz10 is right, you will be given lots of gifts when the baby is born and if your parents/in laws etc ask what you'd like, don't say "oh not sure, some clothes?" this is the time to be cheeky! Direct them to Mamas and Papas cotbeds and point out the one you'd like! (this is what we did and have a £400 work of cotbed to show for it!)
Honastly, it's normal to fret about this. I am having number 2 and will become a housewife so you can imagine the scary thoughts we are having at just one wage!