Remember, some people have budgetary constraints, so affording lots of meat and fish is out of reach for some people. I make enough money, but i'm still kind of cheap when it comes to eating.
So, it definitely is cheaper to supplement with whey protein, my personal favorite being Optimum Nutrition. EAT OR DRINK YOUR PROTEIN EVERY 2-3 HOURS!! This is the most important aspect of weightlifting nutrition.
For fish, that is one of the most expensive things, so i find some other source of Omega 3, such as Flax oil. I don't take enough flax to know if it works. I started taking it for the skin benefits, not for lifting. Oh, and tuna fish in a can isn't very expensive. And hell, it's 32 grams of protein per can! (just don't smother it with fatty mayonaise.)
I don't know what your goals are though, so its hard to give advice. I heard fruits aren't the greatest thing for cutting, cause they have natural sugar.
Vegetables rule! No fat, and perfect for stir fry with chicken or lean red meat!
I know almonds are supposedly amazing for the body, but i'm kind of scared about how much fat nuts have, so i avoid them.
I realize the body needs essential fatty oils, which nuts contain, but is it worth the nutrition if you are trying to cut? If someone could answer that, i would appreciate it.
Nutrition rules. I can finally turn down donuts, and walk through the store and not buy junk food, chips, or Mountain Dew, and it feels great!