Unfair Price Quote for Invisalign? 20 - 25 Trays

If I am considering invisalign to correct structual problems prior to veneering my top teeth and my Dr. told me that invisalign will take between 1 and 2 years to complete but that the cost is the same no matter what. Does that make sense? If they can move my teeth with 20-25 trays as apposed to 40 or 50 wouldnt that reduce the cost? $6200 regardless of time sounds odd to me. Twice the trays would mean more visits and more costs on the Dr.'s part. If we get good results in one year, why am I paying the same as 2 years would take? I'm a businessman and I understand upfront costs for the production of the trays but there should be a reduction in cost for half the amount of trays produced and half the treatment time, right?