What area of utah are you planing to go? It is dependent on where you want to go. Three most popular areas : Park city is good for winter time for ski. I do not know there is tour guide for park city. But it is easy to drive yourself to go up there to have sightseeing. There is famous film festival in winter time producing by Robert Redford. Zion park and Grand Canyon are good fall for this time since it is getting little cooler. Tour guides for these area most likely from Vegas easy. I believe It is about 100$ for person.

Good luck

If you are think about staying with three people, I would recommend Spring Hill suits by Marriott and Fairfield and suits by Marriott in downtown. They have extra living room that has couch ( become sleeping bed ) and roomy for three people. Plus there are free shuttle bus from and to airport and breakfast.
But if you stay any where in downtown is about $8 shuttle bus for a person by expresshuttle for one way. It is not too expensive.

Bonneville salt flats, I would strongly recommend rental car since it is very rural area and nothing there. If you stuck there , you will be so hard to get a ride to anywhere. There is casino in wendover city is very close. Since only 20 or less mile to Nevada. You might have fun staying one night for casino fun if you do not mind loose or win. I think there is speed race in bonneville salt flats I do not know when it is but I believe now like aug.
you need a car to go to bennevile salt flats. I do not believe there is no tour or guide for the place.

Good luck