I can only speculate for you. If you want an exact quote then I would phone a Honda shop. Sometimes independent shops are cheaper and better. My Honda dealer sells automobiles as well, and that's their focus. Their lone motorcycle tech is just a kid in his early 20's with 1 year shop experience.
Checking the valves isn't that big of deal. The front tupperware does have to come off. I'm going to say 2 hours at $80/hr, so between $150 and $200 to check the valve clearances of all 8 valves. Now actually adjusting the valve clearances is a different kettle of fish. Both camshafts have to come out, some micrometer measurements of the old shims are required, and then some math calculations have to be done to determine the thickness of the replacement shims. I'd say another 2 hours + parts (shims and valve cover gasket). So that might run around $400 total, depending on how many valves may need adjusting.
You can't be in a hurry to do this job thoroughly. Unfortunately, most techs are on flat rate or book time. A computer tells them how long it should take an average tech for the labour on a particular job. If the tech can beat that time, they still get paid for the book time, but in reality start another job while still being paid for the previous job. It's in the tech's best financial interest to work as fast as they can.
Please post your actual costs and results when you do get it done. I plan to do my own checking and adjustments when the time comes, as I have a shop manual, micrometer, time, and patience.