[D] Hardware advice for ML rig

In our lab at my university, we are building a workstation for ML. We are little low on the budget, so we are trying make it most cost-effective as possible. We are considering second hand parts. Our maximum budget is 4,900 $. We would be very happy if we get it for less. We have 3 options as mobo + cpu combo:

\-Ryzen 9 7950X3d + X670E

\-Threadripper 3000 series + Trx 40 mobo

\-Intel i9 10980XE + X299 mobo …

advice budget building cost hardware lab low machinelearning university workstation