From the same article here is one idea/guesstimate:
"...The largest anticipated per-unit retrofit cost is for aircraft in LRIP 2, which included 12 US jets, at $16.7 million, based on the May numbers. The estimate from last year projected each unit to cost about $25.8 million.
The cost is expected to slowly decrease until LRIP 10, when each unit is projected to require $760,000 to retrofit over last fall's estimate of $1.1 million per aircraft. ..."