Reverandfunk, amazon has a system where P&P prices are fixed. there is a link somewhere on the site saying what the postage is for everything in list format.. but I can't be bothered to go look!! I think the price for a regular DVD is �1.24 postage. which is pretty reasonable if you ask me :D
ebay can be a pain in the bum, for instance, my last buying experience was with a seller who had almost 100% feedback, I won a pair of shoes and they weren't happy with the winning bid, so they removed their address from ebay, so I had to get it off one of their other buyers through their feedback, they replied to NONE of my emails, this was over 2 months.. I sent payment a total of 3 times, and then had them removed from ebay for being complete tosh..
grrr
I haven't used ebay since.. need to though, I'm in need of some seriously intense internet shopping!