There is no direct air connection to Lagos. The cost of a round-trip ticket is from 65,000 rubles. with one change.
Entry into Nigeria is carried out on the basis of a visa. A visa can be obtained at the consular section of the Embassy of Nigeria in Moscow: https://www.nigerianembassy.ru
The cost of a single entry visa will be 84 US dollars. Processing time is about 7 days.
You must have a Covid-19 vaccine to enter Nigeria. Current vaccines: Astra Zeneca, Pfizer, or Moderna (2 full doses) or Johnson & Johnson (single dose). Nigeria is not in the list of countries where Sputnik-V is recognized.