I'm a nigerian passport holder in nigeria I want to visit a friend in macau

You can apply for a tourist entry permit. First, prepare the required documents including the completed application form attached with a passport-sized color photo taken recently, your passport and copy of its data page, documents of financial support, proof of transportation arrangement such as round trip air tickets, hotel reservation, and your travel plan. Next, submit your application to the embassy of PRC to apply for it.
In regard of the flight costs, you need to find it out yourself.