To compare prices of tractors or guns in the USA with GB is just showing your inability to understand world markets, some things you need to look at
Compare number of guns sold in the UK to the USA, gun dealers import 1000s at a time, the UK would be in the 100s, more guns means bigger discounts
The tractor market in the USA is massive in comparison to the UK, Jd is the main tractor on most farms, also you have to take into account the tax relief given on us tractor sales.
There is also a trade agreement regarding tariffs between Japan and the USA , which does not include the EEC.
all these factors affect new and secondhand goods.