I don't think it can be the retailer? I doubt they make that much margin on these products. Perhaps it's the distributor for Mesa in Europe who is setting the pricing?
Its a shame, I'd love a MESA rig but, even though I could probably stretch to afford one, as LukeRFC pointed out there are so many other quality options at lower price points it's really hard to justify.
Maybe after Brexit we'll agree a trade deal with the US and prices will tumble down