We've done it with Maverick. Flight over Hoover Dam, down the strip with a landing in the Grand Canyon. It was about 3 hours and was $462/person.
It was a great experience that I would recommend. I've not been to the Grand Canyon on my own, so it was great to fit in to the Las Vegas itinerary.
I'm not sure if Maverick will be the most competitively priced, but they met our expectations.
http://www.maverickhelicopter.com/