If sending smaller, lower value items regularly, look into GM Packet via DHL. I just switched to them after getting charged $12 to send a 130g letter, and have saved quite a bit already - contracts will vary but even with my low-ish volume, myself and my buyers are much better off. My costs start at less than $3 to most countries for untracked parcels, and less than $8 for tracked, with no 2cm restriction on thickness - they charge by the gram, and these prices are for very light-weight packages of course, so if your items are on the heavier side this pricing may not be in line with what you'll be up for, but a tracked package to the US via Aus Post is $24 for up to 500g - via DHL I'd pay about $20 for a parcel dead on 500g, with $50 insurance included (insurance is max $50, though, and only available on the tracked packages - it's great for my low value items).
