the above poster is correct, and the reason why Bitcoin isn't a good alternative to western union yet.

Say, a Mexican migrant get's paid his 1000 wage in the United States and wants to send a remittance home to his family in Mexico. He would lose at least 2.5% converting to bitcoin, and then his family would lose another 2.5% converting it back into peso.

The only way it would cost zero is if he got paid in bitcoin and his family were able to spend the bitcoin in mexico instead of reverting back into Peso. That ain't gonna happen never, cause the US and Mexico would never tolerate their currencies being replaced as the default currency for the country.