The only thing you can do is decide how much you're willing to pay to have the bike in your hands and go from there. Sounds like you want the bike, regardless, but the higher charges would sour the deal a bit. Personally, I would start by letting them know that my decision was based upon the total price, that it's not as compelling of a value with the higher shipping charges and that I'm considering cancelling (possibly in favor of purchasing a bike from another vendor). If, at that point, they weren't willing to honor the original price, I'd shoot for a split on the shipping charges (125 euros). If that doesn't work, consider how the experience will make you feel about the bike - for some people, it's less about the money and more about feeling cheated; if there's going to be a tinge of resentment every time you swing you leg over it, then walk away from the deal, it's not worth it. If, however, you can put it behind you it in the time it takes you to crack open and down a beer, then go for it.