Explain pricing for One-off Projects, and credit packs.
See this page for pricing for one-off projects. The top row is the pricing if you pay for each order at order time. You can cat volume discounts by buying credit packs, which are shown in the rest of the table.
Can I mail to non-U.S. locations, and how are these billed for?
Yes. For these we use an international first class stamp.
