How did Oswald afford a trip to Cuba?
Oswald never went to Cuba. He did manage to travel to Mexico City, apparently by bus, where he contacted the Cuban and Soviet embassies to ask for a visa to Cuba. He didn't get one and came back to the US.
I think you mean Mexico City. He took a bus, which is pretty cheap and a long ride from Dallas. FBI even interviewed the guy he sat next to on that bus trip