Nathan,

The price you got for three movers seems to be very decent. Comparing to the prices here in New York City $85 for 3 movers and a truck seem to be about right (I would say the acceptable range would be $80-$100 per hour).  

$175 for four seems to be a bit expensive, although here we should pay attention to the fact that they plan to send 2 trucks instead of one - which raises a question: how big is your move? The only reason to send two trucks is if your items cannot fit in one (unless their trucks are small). In case your move does require two trucks, having only one would delay the move and result in more hours (although I doubt it will double the time...).

In any case, make sure you have few visual estimates before you book with any company, and if you manage to negotiate a flat price for your move then you will no longer care about the hourly rate.