Don't forget to factor in the time it took you to collect/sort those coupons.
The only time I would factor in time, counting it as money, is if it really was a substitute for other time that was, or could have equated to money.
I had a pantry, fridge and freezer fully stocked and packed during my "starving" college days, for literally pennies on the dollar from what the average person paid in groceries, and all because I was systematic about it. This is no idle boast; in the early '80's, my all-time record for savings was $317.13 worth of groceries (two FULL carts) for exactly $16.00.
It's not like it was in the 80's, with price wars and double and triple savings, and multiple coupons, but it's starting to get there. Right now stores like Krogers and Safeway are producing enormous savings opportunities for anyone willing to go online. The big push is to get you to buy in larger quantities, but people of truly limited means aren't spending unnecessary money on unnecessary items simply to brag about how much they "saved". It's all about survival and necessity at that level, with a lot of patience involved. I would buy four copies of the Sunday paper (to begin with) just for the coupons. And more if I needed, if the sales warranted.
One enormously valuable strategy I employed has to do with staying power. In other words, how long will it be before the next sale on this particular item, and can I last until then? I needed peanut butter, but would go without until it went on sale. I never compromised, I had no problem substituting, and acquiring a taste for sale items, so I count ONLY a big sale with substantial savings. And if peanut butter was finally offered at a "Loss Leader" price, I'd search out matching manufacturers coupons (they will ALL send coupons to you if you write to them and ask point blank), and make whatever substitutions I needed to make, to funnel it into peanut butter, so that I could stock up enough to last me until the next sale.
Shop those sales, baby, and more power to you! Get it down to a system and a science. There is no need to pay a lot for groceries if you have the spare time to invest.