sorry, I forgot about school. so its likely friday I would imagine.
presuming con rates are same as last year, cheapest con hotel was 125 a night plus maybe 15% tax. presuming you get friday and saturday nights(leaving on sunday) and then splitting it evenly between 4 people that about 72 dollars per person(rounding up). since it sounds like you guys will take the train, you won't have parking fees either.(maybe bus fees though.)