Is it a good option to go for niche sites??

I am new to the website business.However, I trade in domains.Was thinking of entering into a niche site business.How much does a basic niche site cost if everything such as website design, content etc are outsourced??How much can I make in the next 6 months from it??I am targeting like 100 sites 5 in each niche over a period of 2 years??Any and every feedback is welcomed!!