It's a great time to visit the Grand Canyon, you missed the hordes.
I'm familiar with two, Maverick & Papillon, but haven't had the tour as we drove over from Vegas for the day and.....spur of the moment decided to "go up". It didn't work out - turns out lots of people like flying over the South Rim in the afternoon.
So my tips-
Make reservations
Seating configuration/type, just like aircraft it makes a difference- front facing/stadium style seats are better than bench seats, which is why tours with beach seating are priced lower.
As far as discounts , look at Groupon - 20%