Registered post can be tracked by aus post (just not online) and is only $2.95 for the postage you describe.

Add that on to the top of large letter rate over 250GMs $3.50 plus ebay fee on postage... = $7.10 letter rate, nearly the same as small parcel rate.. The cost is too high for low value items, for letter rate.

The $6.20 prepaid large letter size, I mentioned above includes postage cost and registered post cost with online tracking.