An alternative to using a letter of credit is export credit insurance.
 What are the advantages and disadvantages of using export credit
insurance rather than a letter of credit for exporting (a) a luxury
yacht from California to Canadian and (b) machine tools from N.Y to
Ukraine?

Here is the site of the US government on the subject:
http://www.export.gov/finance/exp_risk_mitigation.asp

and here is one by a commerical insurer:
http://www.meridianfinance.com/credit_export.shtml

If you are asking about one-off transactions, on the first site scroll
down and click on "Short-Term Single-Buyer Policy"

This site also explains, and points out that on-off transactions
usually cost more than a policy that covers ongoing export business.

http://www.sba.gov/idc/groups/public/documents/or_portland/or_exportinsurance.pdf

I expect that the price is not the only consideration.  Claiming on an
insurance policy would be some paperwork, probably a delay in
receiving funds, and  - read the fine print -  may not cover 100%.

A commercial letter of credit is issued by the buyer's bank, based on
the payment and shipping terms and documents required.  You don't ship
until your bank has the L/C.   Almost the only thing that can go wrong
is war or the buyer's bank gong bust.

You can search with "commercial letter of credit" and find more information.