As someone mindful of the cost of protein; canned tuna, canned mackerel, turkey, quinoa, quark (or cottage cheese in the US), lamb's liver (if you can stomach it), lentils, Greek yoghurt, skimmed milk, frozen meats and of course whey protein are things I often mix up.
Also @Fint look to buy in bulk when you see offers and freeze stuff like chicken and steaks, as long as you plan on eating them within a month or so. I have a medium-sized chest freezer in the garage than I bought off a mate for about £40 and I just stick things in there every now and then. Useful reduced to clear stuff goes straight in there, you can judge by eye whether something is going to be ok to freeze for a couple of weeks or not.