Yeah, for cheapness chicken is great, but you really want to work in some variety. Fish (salmon is my go to) is also relatively cheapish depending on your location, and even just a can of tuna in water drained to toss on some salad can break up the monotony.
I also do the occasional tofu stir fry depending on mood. It's light, decent protein, and is pretty much just going to taste like the vegetables/sauce it was cooked with.
Whenever I'm prepping more than a couple pieces of chicken at a time, I always break it up a little bit by throwing 1-2 of the breasts into some light sauce (usually just balsamic vinegar) and letting it soak for a day or two after cooking with salt/pepper/garlic. That way even if I'm just going to be grabbing some veggies and warming up the chicken, it's got a different flavor than just salt/pepper. If you aren't pan-averse, chicken doesn't take long to cook and you don't even really need to add oil if you have a reasonably decent teflon pan. You can then do whatever you want sauce wise in the pan to change things up a bit.
But yeah, you definitely want to look at having some variety in your protein, otherwise it is going to be harder to stick to. Especially at first. Also I can't handle the flavor/texture of brown rice, no matter what is done with it. I'll shift calories around for some calrose or something else, but man fuck brown rice hah.