This is my experience from being in div II but for me, PR manager didn't help much. I first had a superior PR manager thinking it would raise the merchandise by quite a lot but at one point, I was almost making no profit from merchandise because the PR manager's salary was almost as equal to the merchandise sale. (though the merchandise kept increasing) So I got an advanced PR manager with only about 13k or so and the merchandise still kept increasing and I was making a lot more profit out of it. I then wanted to test what would happen with a competent PR manager and the same thing happened, the merchandise sale was still increasing at a certain rate and since competent staff is pretty cheap, I was making even more profit.
But note that I was in a league full of bot and won all my matches, so I guess mine is not the best example but I thought i'd share my experience.