Very few, these days. The Disposable Heroes era was three decades ago.
Also, you are flat out lying. Only the very top franchise in the NFL is worth almost what the UFC is worth. The second-ranked team is worth closer to 3 billion. It goes downhill from there.
In addition, the NFL has 32 teams, each with over 65-70 players who play during the course of the season. The average career is roughly 1.5 seasons. The NFL has a huge number of players who rotate through compared to the UFC.
The players in the NFL play 16 games per season, while the typical UFC Fighter fights ~2.1 times per year.