You can bulk edit your listings, that shouldn't take a month!

What I do know is that I quite often order from large as well as small UK on-line stores and delivery charges are very reasonable. Somehow they seem to manage that.

That is because they probably post offshore on a contract or at the very least if they are a large organisation they will have a contract with Royal Mail. They are probably not posting by a method that needs Paypal seller protection which would reduce their costs considerably.