First of all, my cleaning person, who charges us $170 biweekly for a 2500 square foot house (plus finished basement they vacuum) said the #1 factor that drives the price--even more than sq ft--is how cluttered the house is. If they have to move around a lot of furniture, knick nacks, or clean up your stuff, it is going to cost more.
Also, a 4500 square foot house? $250 sounds fair. Why don't you pay the commoners some money!