Please I need some details about USA VISA.....I want to go there next year and I want to start working on it next month....but I really don't know anything about it....the total amount of money needed and little information about how to get it....

My reason of going to USA is because my girlfriend and her family want me to come and live in USA.....my girlfriend is white...born in Texas....we met last year...but for the past 2 months....she has been telling me to get a visa so I can come and live with her....her parents called me some weeks ago also saying the same thing....

The reason why I asked for help.....is because I've never applied for any visa before....I heard a lot of people and friends who are being scammed by some agent and some...who also got rejected....
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That's why I came here.....I will like to know the roughly amount of money to get both USA VISA and Ticket.....I also like to know about the visa to apply for....
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Because I heard that they have different types of Visa....visiting Visa....tourists....but I'm going to live there for a long time.....that's why I also want to know.....is there any Visa for living in USA for long time period?.....and the way to go about it....like the total amount needed and advice...
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Thanks for your help