@lymenzies ack, the cx3 prices are very good. however, if you want somewhere between 6-8 ConnectX-3 VPI (ie: they do 40G IB and 10G IPoIB) which are like-new in boxes with their cable sets, for free — just cover USPS priority shipping cost (~$15 approx, continental USA).
I learned a lot with used hardware, and really wouldn't have had the opportunity to get to where I am now without that approach. so to spread the sharing-is-caring ethical approach, you are welcome to own them! right now they're hanging out in my hardware stockpile inventory with no intended use. originally I had two of those Mellanox switches for a mini cluster, but I left them at my desk at Fastly just before covid — then they disappeared. cute little blue boxes, very loud fans.
in similar news, I am also giving away other hardware, so if you need other stuff just let me know. if you want low latency more so than RDMA protocols, I have a triple box of Solarflare 10G (see attached), which are formerly very popular with the HFT and distributed computing architectures where PTP time-code syncing is critical for transaction processing without collisions.