rail system on the strip?? Are you talking about the monorail because that is not cheap. (unless you have a nevada id)
A couple suggestions. Someone mentioned the duece, which at times, especially on weekend nights, you can walk faster than, but the Strip and downtown express (formally called the ace and/or gold line) runs the strip and downtown in about half the time, as it makes very limited stops, I beleive only 4 stops the entire strip, plus paying when you board is eliminated, which speeds things up. You purchase ticket/pass on platform before boarding and then just get on when boarding without even showing ticket/pass. Someone on board (not the driver) may come around during the trip and ask to see proof of purchase (ticket or pass) but in most cases no one checks. If they do and you don't have pass/ticket there is a $50 fine, although I have never seen it imposed, just a warning. There are 2 other public transportation, fast alternatives from strip to downtown. 1.) from the lower (southern) end of strip you can catch the airport express line at tropicana and las vegas blvd. It jumps on the freeway and makes 1 stop at outlet mall before arriving downtown. It's about 12 minutes from tropicana to fremont. 2.) from upper (northern) strip you can catch the centenial express at Sands Blvd and las vegas blvd. (fashion show mall and treasure Island) It also jusmps on the freeway and makes 1 stop at Las vegas premium outlets before arriving downtown. Trip time is about 8 minutes. These are both 'residential' routes which have lower fares than the duece or strip express. Single trip $2, $1 for seniors/disabled. all passes are accepted as well.
I might add this airport line is a cheap alternative to the airport as well from the lower strip, (MGM, Tropicana, Excaliber, Luxor, NY NY, ect) $2 and takes 5 minutes as opposed to $25-$30 cab rides. From downtown it is still $2 but takes about 15 minutes. takes you right to airport.
For those extremely thrifty travelers with extra time, you can always catch the free Sam's town shuttle from Harrah or Riveria to Sam's Town and then exchange to the free shuttle from sam's town to Fremont. If you time it perfectly it will take an hour but most times you will have some layover time making the trip an hour and a half to 2 hours.