I got the vivo clamp from Amazon. I just cut my own shelf for the width of my GT Omega stand and mounted it underneath. I doubled sided taped the MageGee 60% keyboard (dimensions, 12.1 x 3.9 x 1.5 )on the shelf underneath the wheel. I have a good amount of leg room. I want to post a picture but I don't know how to do that on here. You don't have to get these items, Just wanted to give you an idea. My friend also used a Laptop tray desk mount, vesa mount with 90 degree rotation. Got it from Amazon. It was by Wali.
https://www.amazon.com/gp/product/B08MN4QFF3/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B092CHWH1D/ref=ppx_yo_dt_b_asin_image_o05_s00?ie=UTF8&th=1
How about starting with a portable display combined with a much cheaper cpu
If size is still a concern, then a portable keyboard, or even a smaller mechanical keyboard if you want something better.
Price-wise, you could probably do better by shopping around, but even this is about the same price as the your other options, just with a proper display and keyboard.