You must be thinking of a different boondoggle, the E-767, which is the obsolete radar package from the E-3 bolted to a 767. The E-7 is a 737.
replyAh right, it's a bit confusing between the bunch of these.
replyNonetheless the price tag was only $400M/ea E-7 for the UK in 2019 (usual later price shenanigans not included)