At $304, I would have paid for the ticket:

25,000 miles + $7.50
vs.
$304 cash + earn 2,800 miles (more if you're Elite)

So you used 25K miles + lost opportunity of 2,800 miles = 27,800.
You spent $7.50 to save $304, a savings of $296.50

Therefore your net redmption rate is $296.50/27,800 = $0.0107 per mile.