I think Nigeria or Lagos specifically is cheaper compare to Johannesburg, my place of residence in Joburg costs me $206 per month, it is no much different from student accommodations, although geolocation also determines just like you mentioned for the case of Nigeria.
Interesting to know a plot of land in Ikorodu is going for $1400, that an opportunity to invest for future gains as the place develops like the Aja, Lekki panned out.
Johannesburg should be the most expensive place in SA, because of the competitiveness unless i'm wrong. Nevertheless I didn't talk about the expenses of living in places like banana Island which is lile probably should be costlier than staying in Johannesburg. However I still believe opportunities lies so much in Places like ikorodu. With 20,000$ you can build a decent comfortable house and could go for More than 100k$ in the Future. Thanks for dropping by my friend.