Mailing lists from a reputable provider can be very expensive though they are almost 100% permission based. If you have limited budget, you can develop your own lists. It is easy. Add a "subscribe" button to your existing pages.

You will have another benefit to manage your own lists. Since addresses are collected on your site, they can be highly targeted. Only those who are interested in your product or service will choose to subscribe. It is estimated that over 80% of subscribers will visit your sites again if you develop a great newsletter and update your site frequently. And, among them, about 60% can be your actual clients.

It is safe to say that ROI for cultivating 2,000 visitors to your site is much higher than sending a million of ads that are not targeted.

Of course, you can outsource your mailing lists to a specific email marketing company. In this way, you focus on keeping your site attractive, and have others done by the outsourcing providers.