How much would a small army of mercenaries cost?

I really want to start a nation and watch it grow and flourish! I would build culture religion from the get go! A new language a new currency! But one problem no real places I can can think of :( But I found that you can actually hire mercenaries that will do what you say as long as you pay! So I will conquer a country in Africa and start from there! I don know how much it will cost so can u please tell me!