Motorcycle parts are duty free into the US. You will perhaps pay some customs fees and this will likely, (but not necessarily), be part of the price you pay them that covers the shipping. Large light boxes are expensive to ship. The shippers use dimensional freight to price this stuff, so it's not about what it weighs, but what size the box is.
We don't have VAT, (value added tax), which is a bigger part of the costs in many countries.