My original assumption was that your Hungarian Orthodox friends currently live in USA. If so, they can just visit surrounding Orthodox churches in the area and check them out. In terms of an attitude of parishioners, it should be welcoming in the majority of parishes. However, they need to understand services, and therefore the extent of use of English language may be an issue.
But is that assumption was an error, and they live in Hungary, may be also these links will be helpful.
Greek Orthodox Metropolis of Austria. As Yiannis mentioned, parishes in Hungary are subordinated to this Metropolis. The contact information can be found: http://www.holytrinity.ct.goarch.org/ecdir.html
Bulgarian Orthodox Parish in Budapest:http://www.rilaeu.com/h1bgeu.htm
Information about Serbian Orthodox Parish in Budapest:http://www.serbianunity.net/yugoslavia/html/churches.html#HUNGARY
Some other links were provided by Ozgeorge.
So, in this case, I would recommend to contact these parishes and to find more information.