that would depend on my mood. If I work hard and have extra money to spend even 10,000 in a few days.
I have well over 700 in my list but that is due to the fact that I have a clickbank product and website, then I give a sample download for free (enter email address and get sent a free sample etc). Sadly I do not utilize my list to full potential due to lack of relevant products on the market. When I do send a mail to the list, then the response is very profitable as I do not bombard them.
from the subscription page in my websites/web blogs.. also buy some leads. you can also use email extractors to harvest lists from the web.
personally i find building lists for clickbank extremely hard, especially if your in those unique niches. you can't really collect opt-in's for things like tattoo products or cure kidney stones or something because there isn't much you can even promote with it. Would be only worth it for those saturated make money products since there everywhere and people are always looking to hit it rich.
I got a list of about 3,000 double opt-ins. I also offer a "Free Sample" for my products, and Email tips on the subject. I have only been using it to promote my own products, and it does a decent job. Interested people sign up for a sample, and receive like 10 followups in the upcoming weeks telling them the benefits of the products and different related info. I don't know what my next move is, as I haven't tried to push any other products to my list. I plan on continuing to build it, and when I get the idea, I'll be ready to put it into action
If your in the Im niche, but also in others you could also think about doing ad swaps. If you want more info on that sent me a PM with your email and well get in contact.
If you give away a product for free you can build to 1000 very fast. Have a landing page with no links, text and only the email box.
Start a blog and offer a bribe for people who sign up to your list. A PDF report or something like that. Tried, tested and it works.