It cost close to €100, but it was h-e-a-v-y. Books, bottles in addition to clothing. I budget that amount just to get rid of the weight. I shipped it from Mail Boxes Etc, which also packed the box (at no cost). They use different shippers, FedEx was a little cheaper than others. Be sure to check their hours by calling the office you want, I went on a wild goose chase in Roma and ended up shipping from Napoli, having carried most of it for an extra train trip (bought gifts in Napoli, so that worked out better, actually).
I have returned from some trips with just the clothes I wear on the plane, discarding everything else! Two tricks: toss some old clothing that you don't want, as suggested; for longer trips, buy a few cheap tops ($8 or less at Meijer) that you don't want to see again after you've worn them 10-20 times.
Lee, no pants?