Two NYU grads and a pal who love living in the Big Apple but don’t want to pay its high rents are happy campers — each shells out $100 a month to pitch a tent in a friend’s Brooklyn back yard. “We’re trying to make ends meet at a time when it’s hard to make ends meet,” said Louis Frank, 22, who set up his $169 waterproof, 4½-foot-by-9-foot tent on a wooden plank in the fenced-in Bushwick back yard on June 1.