I shop really frugally but at the moment I need to lose some weight; in the past I've gone to the Special K diet site for a diet plan but it tends to stack up - £90 for a weekly shop, as opposed to my normal £60. 
We do buy a lot of fruit and veg usually, and eat quite healthily, but main meals tend to often involve sausages/ bacon/ cheese/ insert cheap high calorie item here
I have real problems trying to decide to eat every week even if I'm not trying to diet, which is why I like the Special K site because it just makes everything easy and tells you what to buy.