They will need a passport, and a visa, also I believe they have to do a medical check.
Passport is about 30 dollars unless it is rushed, then it is 110 dollars. A visa will be about 100 dollars. You can buy a prepaid plane ticket.
Please note that 99.99999 percent of all dating from Ghana are fruads, if you read both the Ghana embassy web site or the US emabassy to Ghana most of the entire site is warings about dating schemes.
They have entire businesses that use girls ID's or hire girls to online date with 100's of people at a time.
Normally they will want 100's for passports, tell you they have to have 6000 or more in bank to leave and all sorts of other things.
Ask them to go to the US embassy,
But the scheme normally goes like this, they contact you by email, and in two weeks they are in love with you. They will need a passport and visa and medical, this is almost always 4 or 5 thousand dollars if they think you have it and of course they want it sent western union almost always. After that, they will either have to bribe some official, or they lose passport or it is taken and they have to relace. The will keep taking money till you are out or figure you have been taken.
After that there is no law to enforce and you are just out the money.