As others have said, it can vary hugely but biggest cost comes after 1 year when you need to pay for childcare.
In our case for first year, we spent about £1500 before baby was born - this included travel system, car seat and base, crib, first clothes, washable nappies and wipes, disposable size 1 nappies, baby monitor, electric breast pump, starter kit of bottles, steriliser - basically all the essentials. The only additional things I got after baby cane were a few nicer breastfeeding tops, a good quality breastfeeding cushion and baby carrier.
Our ongoing costs were minimal - greater use of washing machine is the biggest one I can think of. We received so many clothes as gifts and had handmedowns so I barely bought anything. We did maximum of one paid-for class each week, which cost around £8-9 and rest were free children's centre classes. Met up with NCT friends at each other's homes and each brought biscuits/cake along so minimal cost there too.
They don't need much in the way of toys either to start with, a couple of simple things is more than adequate. As they become toddlers, then the stuff starts to accumulate and the toys have the potential to get expensive.
We are incredibly fortunate and managed to save all more than 60% of my mat pay while I was off, which we then used to fund the final 3 months plus a nice holiday.