If I use an Ebay Flat Rate satchel, does that mean it will only cost me about $10 for a 3kg satchel?

[sljudge77]

I posed an item to WA and it cost me $16.30 to send. I just checked out the Ebay flat rate satchels, so does that mean it will only cost me about $6 - 10 to send to anywhere is Australia?  Just trying to find the cheapest and easiest way to post.