This depends heavily on your social position but from context I shall assume you mean the small tenant farmers who were worst impacted by the Famine. I studied this topic under David Fitzpatrick in TCD and the key point he made was that there was no uniform experience of emigration. Steerage tickets were not ridiculously expensive but you would also have to acquire enough supplies (primarily food) to last the voyage and transport to the ports themselves. The total cost would be roughly equivalent to two/three months wages. This money might be earned in a number of ways by selling off all possessions that would not accompany the family to America, the entire family working to send a single person to America (on the assumption that they would find work and send money back for whoever else had to emigrate) or moving to the port cities (like Dublin or Belfast) or Britain and finding temporary work there.

Remittances from those already abroad were however open to less people during the Famine than they were later (the simple reason being that the Famine started the mass flood of people of the country).