$150 is a massive budget for this, tbh. You can do quite well with much less.

This screw is small, cheap, and would be good for a small shoulder vise.

You could also buy this kit and make a Moxon vise, which would be easier to build and could be stored separately from the bench when not in use.

Thank you! Amazon, actually. It's usually called Moxon vise hardware. Here you go: https://www.amazon.com/dp/B084HK7B57/ref=cm_sw_r_apan_i_F7S4B2P2KPEDQJ2SVTJW

It only opens a little right now. I'm considering thinning the jaw down a bit more, so that will widen it. Also, I'm only using this for like edge planing, cutting end joints, etc. I'll have a full blown quick release vise at the opposite end of the bench.