I recently had a ring down sized because of weight loss. The Jeweler I had used charged me $45.00 to resize the ring. There were no stones to be removed. All he did was to take the piece out and closed the ring back up. (he also returned the piece that was removed) My ring was also a Platinum band.
The price will vary from jeweler to jeweler, but it is much more expensive to add a precious metal than to cut and resize a ring where the piece is taken out. I feel that $45.00 is a more than fair price as it should be able to be done in the Jewelry store. With Macy's, they have to send the ring out which most likely costs more because they are a middleman and have to get their cut. I would try a reputable Jewelery Store to have them give you a price. Joan