Leon airport transportation options ???

[The Duck]

Cheap is not always/seldom is Best. But for cheaper even than Don's suggestion and if your friends are traveling light -- and its light out-- they could take a little hike out to the highway and cross over to the other side. The 1st class busses will not stop for them there so they need to head toward the pedestrian overpass just before Col. Nuevo Mexico where the Silao local busses stop. They might get a Metropolitano to GTO with a stop in Silao but most likely a local Silao bus then a Metropolitano to GTO. Maybe 50 pesos per person overall -- and keeping it cheap take a local 5 peso city bus in GTO instead of a 50 peso taxi ride [If your friends get lucky the Metro may continue to Dolores - in that case they could get off near the Plaza de las Ranas or at Dos Rios]

A couple of reasons the Airport authorized cabs are 'expensive'*:1 they are insured 2. they can't take return fares from GTO back to BJX

* JESM you make a good point: at $36 for a 25 minute and maybe 30 km ride it is something you can't do almost anywhere in the US.