Let's assume L's base salary at Miami is $1.2M and Hewitt's base salary is $625,000. That's a difference of $575,000, which sounds like a lot, but...
The average attendance last year was 4,916. The average in L's last year was 5,896. That's a difference of 980. Assuming tickets are $15 (some more, some less) that's $14,700/game. At 14 home games/year (not counting exhibition) that's a $205,800/season difference.
If PH is not kept for next season that's $625,000 we would have to pay, which averages to $156,250 over four seasons. With this in mind, his average base salary would come to $781,250. Add the $205,800 in attendance we lost to the base salary of $781,250 you have $987,050.
So really the difference is $212,950 in keeping L vs. not keeping L.
All of this is without consideration of increase pay for assistants, Patriot Club donation differences, donations to the university differences, hometown discount, sponsorship, etc.
I wasn't a math major so some of the figures may be off a little, but you get the general idea.