Shops charge $80/hr labor in my region and generally round up on time. Changing the oil will suck up an hour (if you want to roll the cost of fluid/filter), the other two hours are to check the valves, hence the $300. Inspecting the valves involves taking a good portion of the bike apart. You can save money on the oil change and do your own and have them check the valves, or you can really save your money and pretend that it's all done and skip it, it's all up to you. But the moral of the story is that you won't find a shop to do a full 600 mile service for much less than $300, if they truly do check the valves. It's not that they aren't being honest, it's the going rate.