If a few decibels louder, no wheels and no electric start isn't a critical issue WEN also has open frame inverter 4000 watt portable generator priced at $300 less than the one in the above quoted link. (An advantage of the open frame gen sets versus the enclosed ones is due to the open frame design internals are easier to access.)
WEN GN400i RV-Ready 4000-Watt Open Frame Inverter Generator, CARB Compliant