It is possible to be stuck in central station if you don't have enough funds for a return trip. Surely there should be an alternate route out of here?
My suggestion is:
Make it a free trip back to a certain destination very nearby Sanctuary. If you paid to visit central, you should be granted this courtesy at least.
I don't think that makes sense at all, when you can't afford to ride the bus they don't let you on the bus.
I would be more inclined for there to be a mini errand(or quest) in the tram station for low level pc's to get a free ride ticket.
There is a quest there - but that isn't a solution.
As I write this, my PC is still stuck in the tramway - and this situation from an OOC game design stand point should be avoided.
You could also think of it as a return trip ticket for going to Central station, HalflingPower.
Would you have taken a raft on Ymph without money to get back?
Make the original ticket cover both costs and call it a return?
As someone who rides the train nearly everyday and in constant battle with poverty, I am comfortable knowing that if I can not afford the ride to the cool part of town, I can always walk...and its free to do so.