via @hpcnotes :
The #1 supercomputer on the Top500 is Frontier at Oak Ridge National Lab, which packs 1.194 Exaflops on HPL and apparently cost $600M.
The aggregate HPL performance of the Top500 is 5.24 Exaflops.
So, extrapolating Frontier's cost/EF, that is a total of approximately $2.6B for all of the Top500 systems.