Woah! That estimate might be a bit high on the upper end. For the box alone ... you have to factor in the permit, inspection, replacing entire service box, new breakers, addition of whole house lightning protector, new ground rod, possible replacement of service line from the street (added amps and old line), possible complications with hookup inside the box.
While you are at it, do you need GFCI's and AFCI's added to meet code? (The inspector might require it).
Good luck and DO IT because you really need the added amps and the upgraded protection.
Just replacing box-for-box with existing breakers is a full day.