This webpage for 16- to 18-year-olds on the official Education Scotland website talks about Emigration and Scottish Society and mentions a scheme that would get a person to Australia for £1 in the 1850s. Before then, landowners wanting to remove tenants to make way for sheep farming funded some emigration.

The webpage is worth a read for an interesting overview of emigration from Scotland.

Some of the first immigrants to America were prisoners or indentured servants. Historically, penal colonies have been of use to imperial powers.

Some were the oppressed religious minority. Fleeing from the Anglican church was enough to incentivize other Christians to leave England. That is why pilgrims are often remembered around Thanksgiving for their travel to Plymouth. These pilgrims often traveled in groups with charters from the monarchy that basically sponsored their colonization efforts.

After the 17th and 18th centuries the promise of a better life in America became more seductive. This was a land free from the tyranny of monarchy and there was plenty to go around under the umbrella protection of a new government. There are not only rich people in the world, so demand for transatlantic passage could even be managed by the destitute if they were frugal enough.

In 1668, passage to the colonies cost about half of Englands per capita income. By 1841, this rate would half again.