As discussed above, March is the cheapest time for plane tickets to Nigeria from the US. Other off-season months include April, May, September, and October. These are good months to travel because they’re not quite as waterlogged as summer, but are cheaper than the winter dry season.
Weather-wise, you will have the most pleasant time if you visit between November and March. These are the official months of the dry season, when you don’t have to worry about rainfall or washed-out roads.
However, be prepared for dusty winds: bring scarves, hats, and protective sunglasses.