Hi kljonsson,
I really know what you mean! I live in Calgary, and I know that the prices are really high here. I do quite alot of shopping at the Northland Walmart. They have a grocery section that is larger than the other stores in Calgary. You can't really buy everything there though, they don't have produce or fresh meat.
My grocery budget is about $600 too. I buy all cleaning supplies, etc. from my that money as well. We have a 20 year old bottomless pit living with us(aka-DS!) so it seems like I am always running out of food. We also have a 17 year old DD.
I try not to buy too many prepackaged items. I make my own cookies, cakes, etc. I find this helps with the budget. I shop at Safeway, Superstore and Co-op most of the time. I buy the best deals at each store and I find that saves me between $30 and $40 a week.
I know this isn't very helpful, but I thought it would be good to know that you are not the only one having trouble keeping your grocery budget down. I think, I have finally accepted that I am not going to find the deals that the American ladies find. I will not be buying 39 cent per pound chicken any time soon!
I think you are doing very well!

I can't find butter for $1.98! The best I can do is usually $2. 25!
Jenna