[quote name='X-Factor611']i was just looking on the usps site and a flat rate padded envelope is $38 to ship internationally.[/QUOTE]
Flat-rate padded Priority for the size the OP is asking about is actually $16.95 to ship internationally. I've had to send a few such packages before.
OP, I'd go with a flat-rate box. More expensive, closer to the price X-Factor posted, but sturdier than the padded envelopes.