What is the cost in US dollars for a Ghana citizen to leave Ghana?

The cost for them is a plane ticket. The cost to you is as much as they can get, since this is a scam.

Alty is right... this is a huge scam. Chances are that it's being done to you too.

Where are they leaving to.

There is a cost of a passport ( from Ghana) and a visa from the country they want to travel to. If the US ( about 330 US dollars total) And a cost of a plane ticket.

There is no other costs for them just to leave the country to visit.

Of course Ghana is the largest nation for internet fraud. The biggest is dating, the second is greed, and the next is ID fraud.
1. they message you from some site and in a week or two, they love you and will want to live with you. Normally they will even take up to two or three months to start asking for money.
** I was given a tour of one of their centers a couple years ago, large office building with dozens of desk and people working 3 shifts. The person you message is often not even the same person every day, but they read past messages and use prepared scripts. They have 1000's of possible scripts to questions or situations you may have.

2. greed, I love these, they have a hidden bank account or gold and have to get it out of the country, but need your help in paying to get it out but they will share it with you.

3. ID, they steal someone's Facebook or other ID and message all of their friends that they are stuck in another country and need money sent.

Normally the key is they ask for way too much money, want to do it illegally

They use fake passports, or passports they steal or buy from locals.
Seldom do they use skype or other video message and have all sorts of reasons not to. And if they do, if they sent you photos to start with, all of a sudden they tell you those photos were fake because they were scared for you to see what they really look like, then they have special girls that do the videos.