I wish to marry a philipino woman working in China, What must I do

I wish to marry a Philipino woman who is working in China. I have been told by her travel Agency that I must send them $6500 dollars in order to get her visa approved to come here to the United States. It is to show financial support for her. Would it be better for me to travel to China and marry her in China or to have her come here to be married. I have already sent money to pay for her visa and for her airline ticket. What should I do next? Why do I have to pay such a large amount of money for her to come here?