My girlfriend is an immigrant and for her birthday, I asked her what she wanted. She said she would like me to send a gift back to her home country for her parents instead of getting her something. I plan to send around $300-$400. Are there any laws I should know about?
If you're sending that amount of cash (as opposed to, say, a gift worth $300), there are no laws, restrictions, or reporting requirements that will interfere with you getting the money out of the USA - as long as the cash isn't being sent as a part of a criminal activity (i.e. money laundering) or to a nation which the USA has heavy trade restrictions on (i.e Iran). Although, even on that last point, there are generally loopholes (you can get special permission to send money to family members in Iran).
However, you need to also check with the regulations of the country you're sending the money to. The amount you've listed is fairly small, but it makes sense to understand if there are restrictions or requirements for reporting money going in to the country you're sending it to, as well.