you need to breed Frontosa in a group preferably 7-9 females and 3 or so males. they do not pair up like CA/SA cichlids.. so, to answer your question it can get pretty costly to get a group this large.
Depending on the quality of the fish you are looking at $50-$100. It all depends on the availability of them, go to a larger city and you could likely get them cheaper. I spent $25 each on my juveniles at about 1" long in my small town, had to special order them. I later spent $9 for same size fish in the city which was three hours away. They also had mature fish for $50 each, they had wild caught kigomas for $150.