Only grainfed meats are available at my High School. Would it be better to just forego them, substituting them, say, with a lot of eggs, or would it be fine if I made their meat a regular part of my diet?
You'll get 90% of the results of paleo even ignoring all the paleo buzzwords. Grass-fed beef is the icing on the paleo cake (which I hear is made out of bacon!)
CAFO meat is better than no meat. I would personally eat more plant foods in this case but its still better. We all need at least some form of meat in our diet for optimal health even if it is CAFO.
Just do the best you can!
Certainly better than nothing. Better than eggs? Well, what are the chickens eating? In general the biggest issue is the fat content. If it's low quality meat then it's generally advised to stick to the protein but trim the fat and try and get more fat from other sources. It's not going to kill you either way, but you might want to consider some variety so you're not eating it every day. Pretty much everyone here probably did though when they were at school and we've survived.
There isn't a whole lot of difference between grain and grassfed beef when it comes to o6. There aren't many polyunsaturated fats in beef full stop, way more in the eggs actually. If you're going to insist on cutting off all those fats, make sure you're getting in sufficient calories elsewhere, whether from sat fats from butter or coconut oil, or carbs from tubers and fruit.
Grain is eaten by animals then it becomes meat. Corn is eaten by animals then it becomes meat. Grass is eaten by animals, then it becomes meat. What do they all have in common...MEAT. Just eat it, don't worry so much about what it ate. Really, try a grain fed meat and green vegetable diet for 6 months...and then a grass fed meat and green vegetable diet (both without eating all the modern, processed, toxic foods yourself)...then get lab work done after 6 months of each... the 2nd 6 months will be better, no matter which meat you ate first.