I take some generic vanilla whey protein isolate. Pic related. From the not-so-flashy packaging, it's not marketed towards bodybuilders so much, but it tastes good and does it's job well. It's about $45 for 66 servings, each at 140 kcal and 30g protein. I typically mix 2 scoops with 16-18 oz of milk. Higher fat milk mixes better imo.
I also eat a lot of eggs. Eggs are around the same price as whey per gram of protein, but the nutrients and cholesterol is very beneficial, much more so than just protein is alone.
If I had the means, I'd eat a lot more meat, too. Meat, eggs, and milk are wayyyyy better than any supplement.