Not many people comprehend how the EU taxes items no matter where you purchase them.  If the sale didn’t originate from the EU the purchased item will be taxed as it enters the delivery system and stop by border customs for whichever country.

Well, it your example, the “real price” should be $399 + Customs clearance fee + VAT. You can either count the US sales tax OR VAT, but not both. Aside from that, from what I understand, the fee to bring non-eurozone
goods into eurozone is a good chunk of change. Plus, since it’s an electronics
product that uses wireless transmission, it has to be cleared by the EU
equivalent of the American FCC or Canadian CRTC, which will also cost
money to the manufacturer.
And to be even more picky, your way is not the right way to calculate the real product price, given that the resellers add ~60% to the price they buy it at. So it’s:
( (cost from GoPro to make it) + (fee to clear it with European FCC) + (cost to comply with label regulations, etc. ) + ( customs clearance fee ) )x 1.6

Note: “label regulations”, customs fees and CRTC are the reason why Apple products are 5-10% more expensive in Canada, cause CRTC has to OK any communications product and all labels must be in English in French, so you can’t just bring a US product into Canada and sell it – it does cost money to sell across the border, even when we are 1) RIGHT next door to US 2) speak the same language and 3) have a free-trade agreement.

Let’s assume that there is a 60% markup on the $399 price. That means that stores buy it at ~$250. Same 60% markup in on €449 => real cost is €280. Difference between $250 (€191) and €280 is €89. That’s how much more it costs to bring goods into the Eurozone.