Getting the screen size in world units

I've seen a bunch of variations on this question, but nothing that quite matches what I'm thinking about.

I'm doing a little CRT simulation and I wanted to start scrolling the text if the textMesh goes off the screen. The easiest way to do this seemed to be checking like this:

 if(text.renderer.bounds.extents.y > SCREEN_HEIGHT_IN_WORLD) scrollText();

The issue is getting the screen height in world space (And, of course, this supposes that the text starts at the upper left, which is fine for me). I can get it in pixels, but not units.

Any thoughts? I could draw a collider around the frustrum at runtime, but that seems like a silly solution.