At 1,000 hours, you may not need to replace all the rubber (belts & hoses), unless they are over 6-7 years old.
Most of these dealerships seem to charge a bit over $100 an hour for service, so I'd guess that it would be $250 plus parts. It will really depend on the Service Techs, as well as what really needs to be done. Accessibility will also be a factor....as to how easy it is for them to work on your particular genset.
Call the local dealership you would bring it to...they can probably give you a pretty fair estimate.