DDR4 is almost as cheap as 3 these days and motherboards like the ASRock X99 Extreme4 are reasonably priced. I got mine for about $150. You may spend a bit more on RAM because ideally you want quad channel but it's not a whole lot more, sometimes not at all more. I got a 16GB quad kit for $60. Quad 32GB kits are harder to find in the $100-120 range but sometimes they're out there.
These quad core Celeron "i7"s having only 20 PCIe lanes will turn into a bottleneck with high I/O devices like NVMe SSDs.