I've not done my homework for a few months, but a couple of years ago...with 2 kids in diapers....I could tell you to the penny what the heavy hitters in our budget cost.
Believe it or not - by hitting their sales, and with "doubling up" by using both manufacturers AND store coupons (they allow it) - Target was consistently cheaper.
Their new "Target Visa" program knocks another 5% off the cost.
Walmart, Sam's, Costco all had *decent* prices. If I was out of something and didn't have the time/opportunity to coupon or wait for sales, then any of those three were my 2nd choices. But, for my shopping needs, Target consistently was cheaper.
My $0.02. YMMV.
Interesting.