My answer concerning men's college football and basketball (i.e. revenue sports), is to use the military pay charts in addition to the student's school tuition, health insurance, and housing.
So,
Freshman - $17,892/year
Sophomore - $20,056
Junior - $21,089 - $23,774 depending on academic credits completed toward a degree.
Senior - $23,360 - $27,198 depending on academic credits completed toward a degree.
5th Year Senior - $25,481 - $29,851 depending on academic credits completed toward a degree.
I think the salary part should be taxable. Also, and assuming you have 100 5th year senior athletes (which is unlikely- 85 football players and 15 basketball players), the budget for salaries is $3,000,000/year. (Is that less than Nick Saban's yearly salary?)
I also think the athlete should be able to sign contracts with the school determining whether they will get a 4 year guaranteed scholarship or a one year renewable contract. For example, Georgia is willing to give me a one year renewable scholarship but East Carolina will guarantee me a four year guaranteed scholarship. Assuming I remain academically eligible, which school is best for me?
http://www.airforce.com/benefits/enlisted-pay/