Cheapest method I used was USPS 1st class Registered Mail which before the latest price increases was cost of 1st class (~$1.75 with DC) + $11.50 registered mail fee. Never had one of these lost, but it can take a while to get through customs, etc.
If it was a free shipping auction, and I trusted the buyer, if the cards < $50-60 USD I normally just took a chance and not paid for the extra services. Unofficially you can trace progress sometimes through the customs #.
Last edited by edhou1; 05-24-2011 at 02:36 PM.