A few days ago I stumbled over this (seems-to-be) fantastic supermarket product (basket) price comparison site http://www.mysupermarket.co.uk/ (UK and US supermarkets) such as UK based Asda, Sainsbury, Tesco, Waitrose, Aldi.... I have only had a look at the UK version and quickly went to check out my favourite supermarkets and had a short research on the different basic products that one would need to get round in let's say a few weeks or so.
The comparison site enables you to parallely compare the total sum of your whole basket of goodies for each individual supermarket and immediately puts the cheapest of the supermarkets on top as soon as the sum changes with a new product. I have to admit that I quickly got lost researching some of my UK favourites: marmite, clusters cornflakes, crumpets *_*....
I thought I might as well run a quick test example for you with a shopping list that might be ours (just simple food and household plus some dog related items - shopping for a few weeks' to month's use depending on the items):
I pretty much included almost all monthly shopping, 113 items, including food (just would have to get fresh fruit, veggies, dairy and bread during the week), cleaning, laundry, beauty as well as dog related items.
It was almost exciting to see the first three shops moving up and down along the listing, I kind of expected those top three (1st Asda, 2nd Tesco, 3rd Sainsbury's) in exactly this line but still, it is really interesting how some shops offer the same products for a significantly higher price.
Here an example with a simple, single product comparison, the choice of product: My favourite Cathedral Mature Cheddar =)
Asda seems to offer the best deal (ignore Aldi in this case, as this shop does not sell Cathedral cheddars, so they just inserted another type of cheddar instead probably).
There is still a lot of research and comparison to be done on my part to see and check how much the results are actual comparisons of mostly the same products - it is not really a proper result for me if I wanted Nutella in my list and the Aldi result shows another cheaper chocolate spread so... still need to check whether it is possible to regulate the search option on this site (and possible favourism maybe....hm, not sure). But in any case, a really great idea =)
Here again a link to the HP I was referring to: