The thing to be aware of is that many, and perhaps even a majority of emigrants to America in that period were not in fact emigrating per se. We like to think they came to the land of the free and the home of the brave with stars in their eyes as hardy emigrants looking for a new life, but in fact they were essentially migrant workers planning on returning home with a nest egg saved up. They became emigrants for various reasons- problems back home, intermarriage, better job opportunities, etc. This is a story that is repeated to the present day- the Mexicans of today are the Italians of 100 years ago, or the Irish of 150 years ago. Thus, it wasn't so often the case that people packed up their households and moved to America.
So, cost. Steamship tickets were the major expense, and were the equivalent of about one-two thousand dollars in today's money. The workers who came to America (and ended up becoming emigrants) financed their travels with loans from labor agents, relatives, other returnees. Steamship companies actually sent recruiters/agents into villages all over Europe to pack their ships with passengers, and it was quite competitive, so the costs wouldn't have varied that much.
Working in America was THE thing to do, to the extent that the steamer trunks the workers brought back full of goodies was called an "America trunk".
If you think of the cost of a non-discount airline ticket to Europe, and money for a month or two of cheap living, you get the idea of what it cost back then- although of course the amounts were wildly less inflated- a steamship ticket cost something like $30.
For a definitive look see: Round-Trip to America: The Immigrants Return to Europe, 1880–1930 Mark Wyman, Cornell University Press
hi! here are a couple of previous similar posts for more responses
How much was a boat ticket from Europe back in the late 1800's?