Your budget and your program needs have a very a large discrepancy. The CPU(s) or GPU alone should cost your entire budget. Professionals drop $2-3k on multi-CPU workstations running quadro or firepro GPUs in them for applications like Maya
Your DDR3 memory will not work with anything new as all of that uses DDR4.
New I would look at ryzen 1600, 16gb of ram, inexpensive mobo, and the best GPU you can get with the rest of your budget.
While there are decent used dual xeon cpu setups, this will be difficult to get in your budget, and your non ECC ddr3 memory wont be usable in this setup either. Anything less than this for used is not going to be better than the ryzen setup i listed above.