Great question Craig, thank you! Some lesser known brands have their place, really only for people who will use their generator infrequently - in which case you can save some money. Then there are also many cheap brands out there that are a good chance to break down on your first starting attempt!
With Yamaha, firstly - their specs are superior; not only are they the quietest and lightest inverter generators in the market, they are also built to handle more intensive, frequent operation. So with a Yamaha, you know it is going to handle your power demands easily and you can use your unit for multiple applications if required; recreation, home power backup, small business, events etc. It is the premium inverter generator brand in the market.
Secondly, with a Yamaha you get a 4-year warranty (which is much longer than the cheap brands) and you get the support of over 200 accredited service agents around the country. Our experience is that the Yamaha after sales support, servicing and parts support is excellent. You don't get a national service network with the cheap brands.
Hope that help explains the price difference, cheers, Steve!