Other costs to consider when establishing your US retail price:
* currency-conversion fee assessed by your bank: I suggest you shop around and find a bank that offers the smallest fee for this "service" and open an account with them specific for your books sold in the USA.
* check-cashing fee for USD-denominated check: Again, I suggest shopping around. In Australia, St. George's bank charges AUD12.00 for this "service," and says it takes up to 60 days for the check to clear (in my case, all US-denominated checks cleared within 2 weeks). Bank of Queensland charged AUD20.00 and sat on my checks for 3 months - only releasing them when I screamed my way up the food chain. That time delay in processing your checks is certainly a cost consideration.
* impact of the IRS' 30% tax-withholding: Mark Coker, of Smashwords, wrote a summary with some good links. You might reside in a country that has a tax treaty with the USA. If so, your US tax may be much smaller than the 30%. Here's the URL for more info:
http://www.smashwords.com/about/supportfaq
Look for the FAQ "Are there tax withholdings on my earnings if I reside outside the United States?"
* Lead the charge to eliminate Amazon's $8 check fee: Pester CreateSpce/Amazon's CFO to get EFT set up for authors living outside the USA (really not difficult). It may be that the World Trade Organization (WTO) at
www.wto.org may have a legal precedent against this uncompetitive trade practice. My high-level search for "unfair bank fee" produced potential results.
I hope this helps. Good luck!