When me and Mrs Nug do the monthly shop, it normally costs between somewhere between £120 and £180 (having said that, £180 only really happens when we happen to see a couple of DVDs that we want

)
That will last us for the full month (including cat food, in case we run out of real food

), but things like bread and milk will add about an extra 20 - 30 quid a month, so it's probably more like 150 - 200 in total.
Mind you, if I add the beer onto that, I think I'll need a second mortgage so I'm not counting that