The good news is that mangosteen grows true from seed. The bad news is that they are supposed to grow very slowly (often more then 10 years before fruiting, but within about 5 years if you are lucky). Grafting has not been very successful so they are generally grown from seed. That's probably why the fruit are so expensive. Very few people here in America have got them to fruit.
I've never grown them but the International Centre for Underutilised Crops web site has all the information you will want to know about growing Mangosteens, plus other tropical fruits (look for manuals and monographs under "Publications").
http://www.icuc-iwmi.org/
Good Luck!