Importing from the UK might be easier because we also have VAT but you might pay import duty depending on whether the cost is above the threshold where it kicks in and whether a focuser is an item that would have a tariff applied. Importing from the US you'd have to pay VAT as well so you might find that once all those costs are added that the cost isn't much different from buying it from a European retailer.
For example if I was buying a $350 focuser then I'd pay another 24% in taxes - 4% import duty on optics and optical products plus 20% UK VAT.
Our tax and duty thresholds are ridiculously low - £39 or less is VAT and duty free, then up to £135 you pay VAT but not duty, and above that amount you pay both.