I see it now.
Correction now, to:
For 4 people. $480 plus seats and bags. Or $2596 plus seats and bags?
Bought the Spirit fare, seats were $36 each.
So 120+36 =156
KEEP in mind, that neither Spirit or Delta guarantee family seating.  So on both carriers, I have to pick the fare category that includes seat picking (on Delta that’s something higher than Basic Exonomy).  And on Spirit, pick the Value (cheapest) fare and then pick+pay seats.
Total 480 fare plus 144 seats = $624. Grand total for 4 people.
Delta ticket for one passenger = $649
4 people on Spirit doesn’t even touch 1 passenger price on Delta, for that redeye on Fri night.       Ouch!