Having looked at this in more depth, the only way I can beat the high street prices on the packaging items is for people to buy in bulk - the more you buy the cheaper the postage becomes. I will naturally pass on any postage saving I make.
In the meanwhile, I have added more labelling items as well as DVDs.
For the DVDs I can offer a postage discount on standard 1st class postage for each additional DVD you buy after the first one. You will only pay £0.75 postage for each additional DVD as opposed to the current £2.45 rate. The first one will of course still cost £2.45 ;-)