I've always rented a car at the Denver airport. It's an expensive place to rent a car, but won't be bad splitting the cost among a group. With 8 people you may need 2 cars, or maybe a van. This far out you may be able to get a good deal on a rental. The best deal I got was $150/week for a small SUV.
There is also a van service to Aspen, but if I recall it runs about $200/person. It may be less if you arrange a charter for a group.
There are some trailheads in that area I would not drive a car to.
If you are looking for less expensive motels in the area, try Carbondale. There are also USFS campgrounds on Maroon Creek Road...