Well, buying traffic "can" be a much quicker way to build a list. But it depends on where you buy the traffic. Much of it is pure crap and you are throwing your money out the window. Usually a sign is if the traffic is too cheap. Too good to true, it often is.
But if you track your traffic, you can tell if a source is good or not.
Now, you could buy it from reliable sources such as facebook. Some people say they do well with twitter. I don't buy traffic so I can't tell you exactly where to get good hits. But FB would be a good place to start. Also depends on what your niche is.
Another thing that is even more important, you need to have your landing page in test mode, tracking conversions, you need to keep improving it. If your buying traffic and your landing page has terrible conversions, you going to be paying alot more for every subscriber because it will take more traffic to get a subscriber.
As far as the money is in the list. That is "some what" true. But, you need to treat them right, you need to build trust, get them to like you, build some kind of relationship, ect. There is more to it than just having a list. Plenty of people who have lists but make no money from them.
Besides paid traffic, you could blog, post to social media, or search engine optimization. Those will take more time.
And for driving traffic, the best way is to generate targeted traffic that is as targeted as possible. Finding people who want what your selling.
Just my two cents.
