Not sure about your state but in PA we have three farm tag rates. They vary with miles of operation, inspection/non inspection daylight only or other than daylight operation. I had my dump registered at 33k. No CDL needed even with air brakes. My tag was for 12 miles away from the farm, daylight and cost 50 bucks for two years. Insurance off the top of my head maybe 75-150 a year through my farm policy. With any of the PA farm tags, you can go a bit further for something like to take it to a repair shop, etc. The big thing is usage must be for your operation. When push comes to shove, they absolutely do not want to see you haul even say one load of stone for your neighbors driveway. Or, using your dozer to grade so and so's lot, etc.
So, plates and insurance can be not to bad depending on your needs. However we license here though, the rig must be able to pass DOT safety checks. Older semi's can be had for cheap but like Russell said, 80 bucks per hour is not. Can you fix it yourself?
That said, I will tell you about a guy I ran with around 1975. I was hauling steel for small fleet owner who was struggling to survive as were the one truck OO's. Due to the length reg's at that time most were running cab over's. This one guy had picked up a White day cab for about ten grand. Small engine even for that time, maybe a 250 Cummins with a ten speed. He had bought well and this little White ran good. He had that paid off and was making money. So, you don't always need the latest and the greatest.