Yea but I have a ton of ddr3 from old setups that I paid only 11-13 per 16gb stick. There's a couple of dual X99 Chinese motherboards that take DDR3 and the dual CPU setup also means unlimited PCIe lanes.Although theoretically there is some limited ddr3 support for 2011-3, I've never seen it in the wild.
DDR4 isn't all that expensive anymore, at least the slower ones like ddr4-2400 are ~$45 for a 16gb stick. A dual E5v4 should have 8 sticks for maximum speed, so, around $360 for 128gb ddr4 ram. Compared to the cost of GPUs that's pretty minimal. The higher speed ram you'll want to use for AMD (ddr4-3200), does cost more, however.