My question is why? Not sure what you have been reading about the cost of 50amp service being more. I guess it depends on what type of park you are staying in. Most standard rv parks power posts have both a 30 and 50 amp plug.
With that said if you are planning on living in it while at school and you want the comforts of home stick with the 50 amp. You will use less propane (water heater) as you will be on electric. You will beable to use electric heater when the temperature get alittle cold. If you were on 30 amp most of that would not be possible.
Good Luck