> Can you tell me why is the range so wide? And are you saying the top end is of equivalent quality, but cheaper in Japan?

I'm not a specialist, but the cheaper frames here tend to be plastic.

The more expensive frames are almost invariably metal, and then the special flexible plastic and titanium frames go for around 10,000+ JPY.

Normal lenses are cheap ("free" with frames), but if you go for fancy ones (bifocals, transitions, blue light filters, ultralights, etc.), the price goes up.

I've almost invariably bought the 4000-5000 JPY frames and they always look nice and function well.

In the US, however, Luxottica tends to control the frame production/pricing, so frame prices are really out of control. That's why other options like generic frames straight from China are much cheaper.