I did a ratio between players and games played in the VFL/AFL:
There were 11237 players and 12155 games played between 1897 and 2002.
This works out to a ratio of 0.9244755 players per game.
I transferred this ratio to all SANFL games from 1907, including all extra games counted from 1971 - Night Series, Champ. of Australia etc.
This totals 8250 games up to the GF of 2005.
Therefore using the above ratio there would be about 7627 players.
However, I would upgrade this to about 8400 or so, due to names before 1907 and the higher turnover of players.