This is just an FYI if anybody else is curious about this: I've been working on booking DONE3 origen WAW, first carrier BA. Sadly, it looks like I'm too late to get it booked during sale, but I thought the price difference might be of interest. Going through the online itinerary builder, the price is USD6681.65 with BA the ticketing carrier. Buying from AA in Warsaw, it's USD 5899.09. So about 25% difference in fees and taxes. Pretty good chunk o change. I imagine the relative difference will hold regardless of what the current price is.