Poly plows actually weigh more because of the additional iron needed to support the plastic.
New plow setups are expensive, which is why we only do seasonal contracts - - - the customer has to help us cover our expenses, whether or not we plow.
2wd is just not a good idea, IMHO. Buy an old used 4wd (late 80's or early 90's) , do some solid maintenance on it and keep it around for the snows. I think you would be money ahead, and you wouldn't tear up a really nice truck.
Also, check w/ your insurance carrier to make sure you are covered for "plow-for-hire" activity. Could be they would walk away from a claim if damages arise from this activity.
Andy