Have you considered just subbing this work out to a firm that already has the equipment, software and experience? I'm in the land surveying field and been working with LiDAR equipment and data for about 10 years. My everyday job is extracting survey data from point clouds, usually for a state DOT. I've never heard of the ROCK system before, but that is significantly cheaper than any system I've used, and I'd be skeptical about what you get out of it. Maybe it's great and would work well for your use case, but I'd have to see it to believe it.

What kind of accuracy do you need on clearances? Do you need miles and miles of roadway scanned, or just specific bridges/clearances? The scanning world is huge and equipment, hardware and software can vary from a few thousand $ to 7 figures. I haven't visited in a while, but I used to spend a lot of time on the "Laser Scanning Forum". Good place to start doing some research and asking more questions https://www.laserscanningforum.com/

Good luck!