Ok, so the dress you have quoted is a formal dress with lots of delicate diamonte beading on the bodice & sleeves which also adds a bit of bulk. It can't be folded up too small that easily without possibly wrecking the beading.  So that postage price includes all the packaging including bubble wrap etc to ensure it's safety in transit.  The box/satchel would have to be a least 50cm wide to allow for the bodice & sleeves not to be folded.  If you have a suggestion on the best way to post this dress safely, I would really appreciate it. The last thing I want is for the dress to be delivered damaged because it wasn't packaged safely. I could probably bring the price down a bit, That is the only dress with an unusually high postage charge.