I am from Mass. and also have a CDL so I have some knowledge on this subject: As noted above, you do not needeed a CDL for that vehicle if its used for personal or recreation use. Farm use also allows for an exemption,no CDL regquied if used for farm purposes; there is a certain mileage retriction (100-150 miles, I am not sure, you'll have to check with farm bureau or the rmv.)
Whether you haver a farm plate or commercial plate, that farm exemption still applies, I believe.
On the issue of farm plates, this farm has had farm plates since they were initiated in Mass 50+ years. However, I have had to re-apply with name change (death). Thet are VERY hard to get now. You need to file copies of your section F tax return, andfd an affidivid from your assesors office if you are under 61A or 61B, or if you are under 5 acres, show your product (greenhouses) ,$ volume. You will also get an inspection by a Registry official (state police) to verify you are indeed a farm, whole paperwork process takes about 6 months. Cost is $100 per registration and $20 per plate (you need a seperate insurance policy for each plate) There are advanatges and disadvatanges of a farm plate.
Most insurance agents/companies don't know how to write farm plate policies and thats why your quotes are high.Farm Family insurance has the absolute cheapest rate for farm plate insurance and even commercial plate insurance if farm related. You do however have to have your farm property insurance with them too. Depending where you are in central mass. there is a office in Northboro, soon to move to Marlboro, but there are offices throughtout Mass.