I bought this one but I'm not actually too happy with it, the arms don't extend as far as I'd like them to. I did look at the Amazon branded mounts and they look pretty good, too. In general mounts shouldn't be putting you back $100, even double arm mounts are very affordable.
Mounts are also very easy to move around in a setup like yours so another reason to do so, IMHO.
Got it from amazon for like ~80 USD Dual Monitor Mount LCD arm,Full Motion Desk mounts for 10"-27" Computer Monitor, /w Gas Spring Monitor arm and Clamp or Grommet Desktop Support https://www.amazon.com/dp/B00V43834M/ref=cm_sw_r_cp_apip_tol3pbPpQcPzu
Thats actually so cheap wtf, it works pretty well for ya?
You are shown measuring a 'frame' that is 3" wide, but I have no idea what it is. If this piece is below the top of the desk by more than 6" then I doubt there's anything that you can buy which will let your monitors attach to it.
If this frame is vertical and not horizontal, it poses another issue.
If the frame is in the way of a 'clamp' attachment, then the only other way that I know of without fabricating your own mounting system, is to either get a desktop mounting bracket which you screw/bolt into the top of the desk, or wall mount the monitors with a dual monitor bracket.
Just an example of a mount that could attach in multiple ways: https://www.amazon.ca/FLEXIMOUNTS-Monitor-Computer-Grommet-Desktop/dp/B00V43834M
Loctek D5D Dual Monitor Mount LCD arm,Full Motion Desk mounts for 10"-27" Computer Monitor, /w Gas Spring Monitor arm and Clamp or Grommet Desktop Support https://www.amazon.com/dp/B00V43834M/ref=cm_sw_r_cp_api_R.WNzbWHT3SQM
Thanks!
Any particular reason you use 2 single mounts instead of 1 dual mount?