Obviously they would range in price depending on the player, type of condition card is in, year of the player (i. e. rookie card is the most valuable), but on average, I would say approximately 30 cents.
Recent football cards have glutted the market. If they are less than 10 years old the average price per card may be as little as one penny. Stars are obviously worth more than common players. Also as a general rule the younger the player the higher the value.