My landing page has an email capture form that I quickly change to match different offers. I need not only a low cost advertising channel, but quick execution (unlike adwords).
Depending on a lot of factors you can make Adwords cost efficient. You may not get the volume you want at the margins you want, but go for margins and utilize other channels to reach volume.
Affiliates can be another low cost but effective channel. Affiliate traffic and conversion quality can be great or terrible. You get what you put in and if you manage the affiliates properly you can get good quality conversions at good margins.
I recommend starting with Shareasale. You won't get the highest volume from them, but you'll likely get very good quality if managed properly.
I'm happy to help further if you want to have a call.
If you're in retail and looking for a quick lever to pull to get a high volume of traffic to your site, I'd definitely recommend starting with Facebook ads. They're easy to set up and optimize, and they're image-based, which is extremely helpful in a retail context.
Adwords is far more complex and relies on people searching for certain keywords - meaning you're either paying a lot more for high-volume keywords, or you're trading volume for quality. Not to mention their text-only format - not ideal. Also, in my experience, display ads get pretty dismal click-through rates.
I'd stick with Facebook (and maybe Twitter) as your first move. Let me know if you'd like to discuss further!
I'd set up Facebook ads because of their robust ad targeting platform so that you can laser focus your targeting which will keep your ad spend to a minimum. Then, I'd use those ads to drive traffic to different landing pages with different offers to see who's responding to what. Then, I'd have each of those landing pages integrated with a different email list in your email provider (aWeber, MailChimp, etc.). I prefer aWeber because I use a tool called AWProTools which offers a lot of features that aren't included in any of the other email platforms. Then, I'd set up autoresponder series in each of the email lists that are specific to whatever type of offer was being presented in each landing page. You can build out your entire sales funnel like this and then just let it run on autopilot.