Congrats to you both
When you do find out if the baby is a boy or a girl, don't go mad with buying the media appropriate colour. If you decide to go for number 2 then you could be stuck with pink hand me downs for a boy.
If you and your partner have parents they will more than likely want to contribute and a small amount of competitive grandparenting is to encouraged and is good for your wallet.
Don't go mad in Mothercare or Mama & Papas. All the main supermarkets do baby ranges, also Argos and Baby R Us.
If budget is important to you, apart from the cot mattress everything else can be bought via the internet and/or ebay and car boot sales.
As with Weddings, there seems to be a premium added on as soon as something is designed for a nursery.
We didn't get a special baby changing unit, I found a chest of draws the right height from Ikea and used that with a change mat on top. To begin with used the top draw for nappy stuff, middle for his clothes and bottom for blankets etc, and then as he grew his clothes took over.
Get a nice comfy chair to go in the baby's room to for night feeds, one with soft arm covers - you don't need a specialist nursing chair.
We started kitting out our sons room from around 30 weeks. But don't go over board with winnie the pooh and other cute Disney stuff. In two to three short years you will be upgrading to a big boy/girl bed and your independent toddler will want a say of what is on the walls of his/her room.