Yet another +1 for bassstringsonline. Great range, never really dealt with the staff, but experiences have always been positive.
Incidentally, are there any plans to offer express or courier postage? I'm an impatient prick, and when I have the option to add $20-30 on to the price to get something in a week rather than a fortnight, I'll usually do it. You're the one dealing with the nuts and bolts of it, so you know best, but if it's something that would be possible it's a service that I for one would probably use.
Although to speak to the OPs question, the only way I've really found to fight postage costs and feel good about it is buy in bulk. It makes it harder to try different kinds of strings on a whim, but it's financially more sound, and means you always have spare strings.
