it probably depends on which postage you want.
Using Speedpost EMS costs like 35 usd (seems to be a fixed rate from their website no matter the weight), but its with track and trace all the way to USA and takes only 1-4 days.
The other method is probably the usual registered bubble mailer envelope kind and its pretty cheap, no more than 8 usd (gotta check again). I don't think it tracks to USA and is probably a tad slower too.