Not true, 8x16GB costs as much as 1x256 on Amazon. The issue here is that Amazon is hilariously expensive in general. Hetzner will rent you a 256GB server for €460 per month. Or you can buy one from Dell for $5000. These are not high numbers, in 1990 you paid more than that for a "cheap" home computer. For the price of a floppy drive back then you can now get a 32GB server.

rackspace, onmetal-memory[1]: 512 GB, $1650/mo (3.22 $/gb/mo)

softlayer, dual Xeon 2000 Series: 512GB, $1,823.00/mo (3.56 $/gb/mo)

these are on-demand prices. pre-pay, or use a term discount, and its cheaper.

Build it yourself: You can build a Dell or similar on a 2-Xeon-proc (E5 series), your main limit is getting good prices on 16x 32GB DIMMS. But lets say you can buy the RAM for ~$6500, then its just dependent on the rest of your kit, lets say $10,000 flat for the whole server. $277.77/mo over 36 months, but you still need network infrastructure, and you might want a new one in 12 months, but you get the general idea.

[1] - http://www.rackspace.com/en-us/cloud/servers/onmetal