Someone will correct me if I'm wrong, but I think anyone from off the street can try to walk on. So an invited/recruited walk-on would be someone that the coach has invited to try out. So your friend's son's classification depends on how the coach views him.
I believe what ClevelandDad is suggesting is that your friend's son get himself into a position where the coach has a chance to evaluate him as to whether or not he could be a potential contributor to the team. First and foremost, the player has to be seen by the coach as someone who can help the team. If the coach likes him, and makes an offer (whether athletic scholarship or invited/recruited walk-on or whatever), then the fact that the young man has reduced tuition is gravy.
We are in a situation where 2B's grades will help him cover a significant portion of his tuition, perhaps even a full academic ride, especially if he stays in FL. So I have been doing a lot of thinking about the walk-on issue, because we are likely to face it if 2B stays in-state. But the fact that the coach won't have to provide a scholarship won't get him on the team. His ability to play has to do that. I wouldn't want him to play on a team just because he's "free." I would want him to play because the coach wanted him there and believed he could make a difference. And then let him try to earn the opportunity to do so.
Don't know if that helps, but there you go.