How much does it cost to ship something from the US to Spain?

Let me clear up a few details, because I haven't been able to find the answer I'm looking for anywhere.

I want to order a pair of sunglasses (pink wayfarers) from a website (http://darrencriss.bigcartel.com/product/sunglasse... but they don't ship outside the US and I live in Spain. I happen to have relatives who live in the US (Illinois and Texas), so what I would do is send the order to their address (either one) and have them send it to me from there. I was wondering how much it would cost them to have it sent to me here in Madrid, so I can repay them when I have the chance. I tried using the UPS calculator, but it doesn't work, when I'm done entering the information it says there was an error and such, so that's not an option for me :/ Also, please don't answer saying to buy them somewhere else or just go to a shop and buy them, because I can't find them anywhere in Spain and this is my best option. Thanks