The first regular steam-service route, from Belfast to Glasgow in 1818, charged 14 shillings¹ steerage¹ - a couple of week's wages for a labourer. The cheapest passage on the Fingal in 1828 cost three shillings. Fares fell to as little as six pence a head as stated in the poem.
Reference:
http://webarchive.nationalarchives.gov.uk/+/http://www.movinghere.org.uk/galleries/histories/irish/journeys/journeys.htm.