- Bridal shops offering alteration services are the best option since they have the expertise and the experience. $219. In 2015, the average cost of a wedding dress alteration is between $184 - $255.1  The complexity of the dress details and degree of difficulty will ultimately determine the cost of your alteration. 2  As a rule of thumb, all alterations should be completed at least six to eight weeks before the wedding. Bridal shops offering alteration services are the best option since they have the expertise and the experience. $219. In 2015, the average cost of a wedding dress alteration is between $184 - $255.