OP, if you want lots of threads on the cheap, you could get a Chinese X79 motherboard, a V2 Xeon, and cheap ddr3. For a little over $200, I replaced an ancient Phenom II 1100t with this motherboard from Amazon:
Lolovi motherboard , a Xeon E5 2690 V2 (10 core/20 thread), and 32Gb of registered, ECC ddr3.
You should be able to find registered ECC ddr3 on Ebay pretty inexpensively, and the 10-core 2690 v2 is about 60-70 on Ebay, or the 12-core E5 2697 V2 for about 75-80.
If you don't mind buying from AliExpress and getting a mATX motherboard, here is a nicely-priced combo:
motherboard, 10-core Xeon, and 32Gb of ddr3 for under $200
These systems will not blow your socks off compared to modern systems, but they give you alot of threads for the money.
Or, for about double the price, you can get two of those CPUs on a dual-socket motherboard. It looks like the core/thread count is a little off, but this should net you 24 cores and 48 threads for under $500. I believe Gamer's Nexus did a review of a similar motherboard.
Dual-socket Xeon goodness