How much money would it cost one person to leave newtown ghana to come to seatac airport to visit?

It won't cost you a thing if you don't succumb to this very common scam.

This is a scam.

Please read: https://www.askmehelpdesk.com/visas-passports/ghana-romance-scams-442160.html

Ghanaian passport $130 - $230 depending on application type. US visitor visa application fee, $140. There is no Ghanaian declaration fee nor is there any US visa reciprocity fee.

If she is asking for any money at all, likely to be a scam, please be careful. Good luck.