Lets face it, it's difficult to plan what to eat for a whole week and not many people do it. My partner takes care of meal planning and shopping lists to save us money so we don't wand aimlessly around the shops buying things we don't need and forgetting things we do need.
Concise meal planning could be a freemium web offering where you can specify a budget and a real person or smart algorithm will generate a meal plan for you, approximate cost within budget, dietary requirements and a shopping list. Integrate this with shopping data from actual stores and you've got a web service.
Obtaining cost information for a users favourite store could be difficult. People rarely plan routine meals, so a smart algorithm might be able to generate meals to an extent, but could end up generating meals you don't even like.
There are no precise existing solutions. There are dieting programs like Atkins, Jenny Craig, Weight Watchers and whatnot which do offer calorie controlled meals and recipes, but rarely recommend you meals and don't generate a shopping list with price estimates.