Free hotel shuttles are something that we've been listing for some years now and it's a continual work-in-progress, as routes, schedules, and property ownerships all change on such a regular basis, keeping up is kind of like painting the Golden Gate Bridge.
Most hotels offer their guests a complimentary shuttle service from/to the airport, so we take that as a given and don't list all those; what we do list are those shuttles that are prepared to carry non-hotel guests and that link different properties in a casino group, or which take passengers to/from outlying "locals" casinos to the Strip or downtown, or casino shuttles that will drop you at various shopping outlets, for example.
Since it debuted in 2009, M Resort's shuttle policy has vacillated between being free to all, being hotel-guest only, and, as it currently stands, being somewhere in the middle, where guests get priority access but non-guests can catch a free ride, space and driver inclination permitting.
There isn't an RTC bus service out to M Resort; the #117 Las Vegas Blvd. S./Silverado Ranch route goes out that way, but it doesn't take you to the resort itself and, with the recent spate of pedestrian fatalities caused by tourists attempting to cross the freeway and other such kamikaze behavior, we are certainly not going to advocate anything that involves walking in areas that aren't designed to cater for pedestrians.
That pretty much leaves a taxi as your only other means of getting out to M if you don't have a car. The bell desk at the resort estimated that it would cost you around $40-$50 each way from the Fashion Show Mall, so you'd actually probably be better off splitting the cost of a rental car between you, if one of you is prepared to be he designated driver.
Bottom line, if it's not a particularly busy day, you stand a good chance of being able to use the free shuttle in both directions; just be prepared to be flexible with your travel times, in case the bus is full.
Click the link for our full list of Las Vegas' free shuttles (a list that's much diminished since the economy nosedived), which we just updated. It includes printable maps with pick-up/drop-off locations and times.
