ermm... I have no idea hun but at best it depends if you spoilt them rotten with needless toys etc in the beginning and clothes etc.
I'd have to say I spend about £10 on nappies a week (including wipes)
£10 on baby jars a week
£10 a week on milk
I'd have to say thats an estimate I generally buy bits all the time. Thats not inclusing the toys I get him the clothes, the energy used to heat up food, keep him warm, wash his clothes etc.
Its not cheap but you find ways I barely get myself anything anymore.
My OH is selfish and pigs out on crap food alot so I generally take most of the money off him.