If you are taking a trekking trip then I assume you are going to drive to the South Rim. Great trip up and down, a lot harder than you think it's going to be, take lots of water and anti inflamatories..
So, if you are already at the South Rim, Grand Canyon airport is only a few miles away. There are tour operators based there who will take not much more than US$100 each and take you for a flight. It's a lot cheaper than the prices you see from Vegas. You also really need to stand on the rim and look down, and for that you need to be on the ground. Just flying over from the air only gives half the story.
Given that you are assumed to be at the rim anyway, I doubt you could do it cheaper yourself once you have factored in the checkout, bit of mountain training, and flying to and from the canyon itself. Also, you talk about fellow trekkers, so if you are going to load the plane close to gross you will need far more than 160hp, or even 180 to get to the minimum altitudes in the SFRA. If you are four up, I'd take a 182. Now you are into high performance which requires an endorsement, and probably a few hours dual to keep the insurance company happy.
Of course you could take them elsewhere in a 180hp, and be lower, but when most people say they have done the canyon it's through the SFRA corridors. Those are 10500 one way, 11500 the other. Remember in the mountains excess power is especially nice to have (as elsewhere of course)
Anyway, plenty of choices, and the other nitty gritty has been discussed before.