I do quite a bit of international shipping, and the answer is that it really just depends. There are several different factors at play. Some will not even ship international, because filling out customs forms, etc., makes them nervous.
Does the shipper want to take the trouble to find a box of the approximate size of the item being shipped, weigh the package, and calculate the postage? This is usually the cheapest route. However, if the weight of the package is over 4 lbs., the Flat Rate packaging starts to make more sense in terms of cost.
Is the shipper looking for the most convenient option? Which is to say ship everything in Flat Rate boxes of the appropriate size. Flat Rate boxes are more expensive, when the package weighs less than 4 lbs. But some people don't even know this information.
The cost of postage for a Large (Board Game) Flat Rate Box shipped from the US to Bulgaria is $78. That is the only Flat Rate box that will fit a full-size keyboard. And if the shipper wants insurance, that adds another $5 or so. Even a Medium Flat Rate Box, which won't even fit most TKL boards in their original boxes, now costs $60 for base postage. You have to remember that international postage rates recently took a large price hike in the US for whatever reason. There is nothing we can do about the increased cost of postage, unfortunately.
I doubt the $35 you heard is with the current rates. I shipped a couple Pokers recently, one to Norway and one to Australia, and the base postage rate (by weight) was over $44.
