130 teams with 85 scholarship players each. So 10% of an average scholarship roster is about 9 players. If you throw in redshirts, etc. that interrupts the numbers, but that's a separate category of players as far as most are concerned.

About half of those 130 teams are G5s who will probably have an average of about 1-3 players each with serious NFL potential in a given year spread across all four classes (freshman-senior). The other half are P5s, each of whom will have an average of 15-20 players every year with serious NFL potential, spread across their four classes.

Combine those averages out over the entire pool of 130 teams, and you end up with 10% of FBS football players in a given year who can be considered serious pro prospects - thus having some viable economic value outside of their college affiliation.