I think it truly depends on what you are buying. If you buy a lot of frozen dinners like Lean Cuisine, or diet products like low carb bars or Skinny Cow low fat ice cream-then yes it can be very expensive. The only time I buy expensive things like that is with a really good sale or a really good coupon.
The way I see it-is I can spend $3.00 on a small container of fresh blueberries or rasberries...but I used to spend that same $3 on a bag of Cool Ranch Doritos. (And in my case both are completely eaten within 1 day.)

So for me I can eat just as healthy with same cost as I did when I was eating badly.
For me some things are actually cheaper-the $6.00 24 pack of Coke or Pepsi is now a store brand 24 pack of bottled water for only around $4.00.
Some things are actually pretty cheap all of the time-bananas are usually .50 a pound or under...you can get a bag of apples here in Indiana for about $2.50-$4.00, my store sells kiwi fruit 3/$1.00. If you buy brown rice in the bags (where you actually have to cook it for a while) rather than brown Minute Rice, or "heat and eat" type brown rice packs it is really cheap too. Oatmeal is cheap.
I think it is important to check the store ads before you shop-I buy whatever fruit is on special that week. They had a sale last week for a flat of strawberries for $4.99! (equal to 4 pints that are usually $2-$2.50 each) When they are in season-fruit like watermelon, nectarines, and peaches are uber-cheap as well. Just check the ads.
When boneless, skinless chicken breast is on sale really cheap I stock up and get a couple packs for the freezer. I also do the same with frozen vegetables.
Clipping coupons is another strategy that I have-my store doubles them. It really adds up-I save $5-$20 a week in coupons.