I suggest you start an ezine in the niche you have chosen and get a PLR product that you can offer to all in exchange of their name and email address. And not to sound repetitive, Aweber is the way to go. Then, get a squeeze page to gather your leads.
Once you have this setup, join a giveaway event where you can offer your free PLR product to all interested in your niche. This is the fastest, cheapest and most reliable way to build a list to start.