After seeing that tandyleather.com has their straps on sale for $8.99 plus shipping and one or two similar items on ebay are being sold for around $6.00 plus shipping, I've decided to ask for $5.50 each strap plus shipping. I haven't found a USPS option cheaper than $6 and nobody else seems to have either.
If you want to make a purchase of several at once I am also willing to negotiate further discounts.
Cheers.