Where I live, revenue from fares makes up ~11% of the total. (The largest chunk of revenue is from local sales tax.) Making transit cheaper would be relatively painless and highly effective: we have a 'free fare day' every year where 25-65% more people board a bus or train than on regular days. A new frequent bus service connecting train stations and major destinations sees as many boardings as existing light rail; it is free to ride.

A small sales tax hike is palatable to enough people that it is politically viable, whereas a $2.50 fare every time you board a bus or train makes more people not ride transit who otherwise might.