Officially, merchandise can only go as a parcel, and the weight brackets for that are up to 250g, up to 500g, up to 1kg etc

If you send enough parcels on average to qualify for discount, purchasing postage via My Post is your best option (eg I'd currently pay around $17 to send up to 250g to the US, if you send 10+ international parcels a week you can inquire about an eparcel contract just for international orders, which is even cheaper but you forgo things like insurance (it's available but costs extra whereas regular postage includes up to $100 by default-for low value stuff it's probably worth the saving and no insurance). A colleague of mine pays around $12-$13 for their US parcels with this option). 

https://auspost.com.au/business/shipping/parcels-international/contract

Whatever you pay, whether or not it's worth it is kind of subjective, but in my experience usually when someone starts asking that question the answer tends to be no lol. But at the end of the day it doesn't cost you anything to make the items available to international customers, maybe a few extra headaches I guess in some cases, it will cost you more to sell  to an international buyer, but if you do the math well enough and charge appropriately, the buyer is the one who should be paying the extra costs and the one who decided whatever the cost was worth it to them. Just keep an eye on international regulations; US may potentially be problematic to ship to right now, EU countries are usually more trouble than they are worth as well, with GPSR and packaging directives and the like.