the above link suggests tens of millions only in FY2018
That SLEP is a stop gap fix and only addresses the most strained structural member the Longeron.
It doesn't touch any other members including the second most warn portion the Wings.
As the article it's self states
replacing the longerons on the fighter – an endeavor that would cost about $1 million per aircraft – Boeing could push the F-15C's service life into the 2030s.
An earlier USAF analysis examined updating the F-15C’s fuselage, wings and landing gear, which could stretch the aircraft’s life into the 2040s – but would cost $30 million per airframe
It makes no upgrades to systems. So basically they fix the Longeron and nothing else $1 Million.
You start addressing the other old parts $30Million.
But add in
that "Vapor" being system upgrades that merged to be part of the F15x and had been demonstrated if not proven on F15 in foreign service and at home or other air craft.
Passive Attack Display, same type found in Super Hornet block III and F35.
Already found F15SA and F15QA was demo'd in F15C 2015. They also demo'd the Sniper pod. Legion pod demo'd in Super Hornet block III and F16C Agressors.
Talon HATE pod to add Data link with F22 trailed in F15C in 2015.
Eagle Passive Active warning Survivability system flying on F15E, F15QA and F15SA.
New wing structure flying on F15QA.
AMBER weapons Racks. F15QA
FAST pack CFT on F15E and Strike Eagles globally.
Radar upgrades found on F15 globally.
JHMCS II on F15 of the USAF.
In FY2017 Boeing won a 95 million dollar contract to upgrade radars on C, D and E variants. The year before they won a Half Billion dollar contract to upgrade the radars and add FAST packs to 71 F15. But that was not including additional upgrades and structural changes.
F15CX and F15EX would replace between 80 to 144 F15C and F15D.
My math at 40 million a bird is north of 5.7 Billion assuming nothing else went wrong.
