I got my most recent from orbital https://orbitalcomputers.com/ The one before was from cyberware , gave away still running after a decade like new. both ssd 6 monitor capable only ever used 3. You could probably build one cheaper yourself .
For the last several years, the "going rate" for a very competent-for-trading, 3-yr old workstation from Dell, HP, or Lenovo is ~$350-$400. No need to pay more than that.
Best kept hardware secret, get yourself a Lenovo m92 or m93 Tiny with SSD. around $200 on ebay. Spent the $ on a mechanical keyboard , mouse and monitor(s) , office chair and desk.
The best place to get Day Trading Computers custom and cheapest is mytechcompass.com .. Just bought a whole new system compared to all the other places at least 20-30% off..
out of the box 5 or 6* monitors , (4 from the display port daisy chain + 1 VGA/DVI + *1 HDMI option )
With Display port you will have only 1 video cable from the computer to 1st monitor than from monitor 1 connected to monitor 2...( very clean set-up)