We are a lean startup, looking to test our product with a few users. Not looking at large scale traffic, 50 users a day would suffice. Anything above a 100 would be detrimental.
Facebook marketing would also be a fast way to get you traffic -- and it is especially targeted. You can aim at a competitor's page on Facebook and only message to their followers. Should be a fast/easy way to get traffic to your site.
BTW, if all you need to (50) people per day, why not message out on social media? You can't control the traffic once it get's going. It's a double-edged sword. :-)
Also: Quora, Clarity, Angel List, LinkedIn Groups, Stack Overflow, etc... (Those are all free to engage!)
