Mu guess, your jewelry will weigh package up about 2 to 5 oz. When I ship everywhere else UK and as far as Australia at 2.5 oz, the postage for first class is $4.56. You may want to add extra $1 or so for packaging / handling. Or you can do like Judy does... ask the buyer to contact you so you can give a more accurate rate. Of course you need to have a scale at home or has access to one. My local post office has a public scale, anyone can use it for free.
Or you can also send flat rate priority. I used priority a while back but realized I got more international sales when I opted for first class. Just lately an item lost during holiday season, I reshipped another one. I don't have any clue where its at because there is no tracking for international first class. The risk is quite minimal so I finally go with first class. However when I shipped something over $100, priority insured, is the best bet.
Hope this helps