This is an opportunity for who wants to fly to Mombasa with the last flight on 24/10: JetAir sells a one-way ticket on SN479 for only 99 EUR, airport taxes included!
The last return is unfortunately more expensive: 249 EUR on the same day!
I would guess that SNba charters its plane for a fixed rate they agreed upon with JetAir. So it doesn't matter to them how full the flight is or how much JetAir sells the tickets, they should still get the same amount of money.