Do mean do it yourself or pay to have it done professionally??
Unless you have an industrial machine, I can't imagine a machine that can handle a jeans waistband. Then there's the fact that it's a difficult task, jeans aren't cylinders, so there would be a mismatch between the circumference of the band and the new lower circumference of the jeans. Then there's the new zipper length.
So if you are paying someone to do such a finicky job, it's going to cost you quite a bit because they'll need to have both the skill and the equipment to do it, so they'll be expensive.
Are these $600 designer jeans? If no, just find a brand that fits you better and buy those instead.