Going the Threadripper road here costs you -at least- a mobo, the $339.99 Asrock X399 Taichi as most economical choice gets my recommendation here.
A few years ago I never thought I would ever recommend Asrock, but they have some rock-solid boards nowadays, and never shrink away from being the only supplier in a given niece (e.g. Socket 478 with DDR3)
You need a Threadripper too, and that 12 core is gonna cost you some $799.99
I'd buy -at least- 96GB of ram in a 24-thread sytem. A 128 GB G.Skill quad channel set sets you back some $1,170.99 though...and that's the cheapest option at Newegg.

$339.99 + $799.99 + $1,170.99 is some hefty $2,311.....

What does socket G34 offer?

Don't ask me why, but Newegg has a hard to beat offer: an OEM Dell DW8Y5 Dell PowerEdge C6145 Server Quad Socket G34 for $113.90 . No need to fill them all at the same time. I'd say...
Two Opteron 6338Ps for this mobo will cost you $392.37 each at Newegg and two sets of 48GB of Crucial Registered ECC DDR3 RAM will cost you $489.00 each,
-> grand total $1877,00 for the G34 that has only half its sockets filled. Not too bad. Hard to make a choice here, especially when you already have some G34 hardware lying around.