I had a similar belief a few months ago, especially when I was low on cash. My issue was this: I sell stuff on eBay all the time, and I ship stuff all the time. For small items, especially small and light items (read: XL pads), you can ship very inexpensively. USPS First Class Shipping is always under $2, and that's for me, so if you're a big company with a contract, you could probably get that even cheaper (or that's just how it worked out in my head, that's really all speculation). So, paying $5 seemed ridiculous to me. But I got a job, and I started using my headphones more, so I coughed the money up. I don't regret it, although I do think that shipping is still overpriced.
As for the price of the headphones, I do not think they're overpriced at all. You have to take in so many factors when figuring out a price, part of which includes the price of your competition. For all you get on your M100s for that $300 price tag, I think it's plenty worth it, especially when the all plastic competition is selling for the same price.