This strikes me as an impossible thing to judge without knowing more about your life. You say £200 after bills, but what do bills cover? Do you mean council tax, electricity, gas, water, insurance? Or are you covering phone, tv licence, car tax, etc too?
I have spent many years as a SAHM. Dh has a well paid job, but we have larger than average outgoings in that we have 4 children and a larger than average house. Some here would think we are wealthy, but often we only just get by, just like seemingly poorer households. This is how I worked out how much are outgoings were so I could ensure we stayed on track:
I worked out all our annual costs and factored in an average weekly grocery spend. After everything foreseeable had been accounted for (including a bit of pocket money for the children, kids activities, subscriptions, etc), I then calculated £400 a month for one large expenditure eg car service, Christmas, car taxes, car insurance, house insurance, school shoes x4, holiday savings.
I think, after all our regular or expected expenses were accounted for, we had about £200 a month 'spare' - in theory, but in practice, if often seemed to be absorbed into regular costs.
I think you would do better to work out all your costs, and see what is left over. After all, you know you are going to buy food every week so why not account for it now?