Postage questions

I sell plants and before packaging I don't exactly know how much they weigh.

So far I used the ebay feature for Australia post.

I find that the value of what I send is poor compared to the postage. And sometimes the ebay feature does not work out well for me.

Furthermore I cannot charge for packaging.

How do you do the postage?

Are other carriers cheaper? I need a carrier which is as fast as Australia Post and reliable and I am not in a metropolitan area.

What is the advantage of e-parcel? They don't really say on their webpage.