Wired's travel blog Autopia breaks down the costs to check extra bags and it turns out, you can save money by shipping it instead:
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I think checking it would be cheaper
I also think that checking would work out cheaper but possibly not a lot cheaper. I moved to Bulgaria last year and because I live in Canada I had to ship everything over. After reading an interesting article about removals to Bulgaria here http://www.questbg.com/property/buying-selling-renting/2260-removals-to-bulgaria-top-3.html
It helped me with the decision of how to get my belonging over in the cheapest possible way.