A good example of a food that varies widely due to how it's produced is the humble egg.
I can very easily tell the difference between the organic omega-3 eggs I purchase at Costco (about $4.50 for 18 eggs) and the "regular" grocery store eggs.
For one thing, the regular egg is much thinner. I could easily crush it in my hand, and the shell would just disintegrate without causing me discomfort.
If I tried to do that with one of the organic omega-3 eggs, I'd end up with some painful, hard shell pieces poking me. I think I'd be afraid to try it, honestly. The shells of the omega-3 eggs are at least twice as thick as those of their conventionally produced cousins.
Conventional egg yolks tend to be pale. The organic omega-3 eggs have a much darker, firmer yolk that stands up well in a frying pan.
Remember that "free range" and "cage free" don't necessarily mean the egg is any better for you or for the hens. The hens might have been treated well -- or they might not have. They might have been outdoors -- or they might have been kept indoors the entire time with no access to bugs and other healthy morsels.
In terms of egg quality, it means nothing at all.
Check out the Food Renegade's guide to eggs for more detailed information on what you should look for in an egg.