As far as I know, there were only 5 PPro computers that could take >4GB: Axil Northbridge NX801, Data General AV8600, HP NetServer LXr Pro8, NCR Worldmark 4380, or Unisys XR/6

Interestingly, while the Intel 450GX chipset was designed to daisy-chain DRAM controllers (1 controller chip per 4GB of RAM), none of the boards that actually could take >4GB used that, instead building their own solutions. Presumably that meant that there was a bug in the chipset.

Anyway, each of those 5 computers would have run you at least $500k in 1998.

(I've been on-and-off trying to acquire one of those boxes for a few years now.)