Hello!
Im sorry this is a late reply but I noticed that no-one had so thought I would! Although I live in the UK it took me quite a while to sort out my postage and packaging. Like you I ended up paying far more than was necessary.
First thing is to find a suitable postage box for each of the items you offer, do not deviate from those boxes. For instance I know my medium postage box will take 6 of my standard roses. The large postage box will take x number of giant roses. etc.
The next thing was to take those boxes to the post office and get a set price for the size of the box. The paper flowers weigh very little so the price remains the same whatever the number of flowers you put in there.
I hope this helps in some way - but sometimes its nice just to get a reply isnt it!
Good luck with your business!
Cathryn
PaperalchemyStudio.etsy.com