I just read a statistic that said that only 1.6% of college level players will get drafted into the NFL. And of those who do get drafted, how many are good enough to last in the NFL for a few years.
Division 1 FBS is a good bit higher than that.
130 schools x 21 scholarships per year = 2730 players.
Division 1 FCS is 63 scholarships / 4 = 15
1500 more players = 4230
Not every FCS school uses their full allotment of scholarships.
With walkons plus Division II, III, and schools not playing a full schedule there could be as many as 16000 eligible in any given year.
However most of the 256 drafted are going to be Div I FBS.
So for them it’s maybe 8%. Div I FCS chances are a lot lower, and Div II/III, etc. are much lower.