There a number of triple arm mounting systems available.
For example:
https://www.staples.com/Mount-It-MI-763-Triple-Monitor-Desk-Mount/product_2093765
There are more expensive products available and those are more likely to be stronger and better quality. Easier to install, move, and adjust.
You should use a clamping system but be sure that your desk has an available edge to clamp to.
And I am wondering about the requirement to move the middle monitor up and slide the left and right monitors to be side by side.
Is the middle monitor to remain on? Why not use just some pairing like the [right and middle] or [left and middle]. Leave the "3rd" monitor off.
Raising the middle monitor (especially if to be used) will require some extension on the middle post which is likely to make the assembly less stable.
A monitor mount similar to the following may be more applicable:
https://www.staples.com/Mount-It-MI-753-Triple-Monitor-Desk-Mount/product_2093778
But would require some sort of gooseneck (up and down) arm for the middle arm versus the lateral left and right arms.
Putting that "all together" and googling (include "gooseneck") I found:
https://guide.alibaba.com/shopping-guides/monitor-desk-clamp.html
Check the Cotytech offerings.
Unable to comment regarding the price as "outrageous" or not.