With OnePlus available across several countries, I have done a comparison of a handful of countries for the cost of OnePlus 5 and OnePlus 3T.
I have used the base currency as INR (Indian Rupee) as the OnePlus brand is hugely popular in India. It becomes apparent very quickly that out of the four countries (Canada, UK, US and India) US is the best place to buy the phone and you will have to shell most amount of money if you buy any OnePlus phone in UK.
In UK, OnePlus 5 6GB model is a whopping 25% expensive than US. Other countries and models have smaller differences. So if you are a OnePlus fan travelling to US for few weeks, you know what to do.