how much does it cost for staying at usa for 6 months?

Figure the barest minimum would be USD100/day for 180 days - that's $18,000. That's just for a very modest hotel room, some food. $200/day, except in California, New York City, some other high-cost cities, is far more reasonable for hotel and restaurant meals. That still doesn't cover sightseeing, entertainment, your round-trip airfare, and other typical tourist expenses.

Depends on where you stay, $30,000 could get you a nice living in most of the country, while $200,000.00 will just get you by in New York or LA.