Is online advertising cheap?

To Understand online advertising requires your marketing knowledge. If you ask "advertising online is cheaper or expensive compared to the traditional media advertising?" you probably don't understand Marketing. In general, Marketing is not about cost rather its about return on your investment. When you are thinking of online marketing, you should have a goal. For your online marketing campaign, the expectation is to get the best ROI (Return On Investment). If you spend a high amount of cash for a TV ad (Traditional Method), you are not likely to get a good ROI. On the other hand, if you run an ad by using an online advertising channel, the ROI will be good enough. Online advertising will give you a good ROI, but why?

In online advertising, you always have the option to track, judge based on your spent and what are you getting from in return. I believe you already understood what question should be asked instead of "Is online advertising cheap or expensive?". Yes, you are right. The question is accurate if you asked now "Is online advertising effective and profitable?". The answer to this question truly depends on the data and various studies. Look at the available studies and reports on the effectiveness of online advertising against traditional advertising. You will get a reliable and specific answer. 

What if when you need your answer on "Is online advertising cheap or expensive?" The answer is "Yes" always. Traditional advertising approaches are expensive. If you take a look at newspaper advertising compared to advertising on a webpage, you will get a more specific answer. So, what is the metric to use for comparing whether it is cheap or expensive? Now come to the main point. Generally, online advertising pricing is happen based on CPM (Cost Per Thousand Impressions). There are other pricing models too, but CPM is more common. Now search on google for the latest CPM cost for Google Ads, Facebook, TV, Billboards, etc.

I hope the thing is clear now. Thanks for reading my personal opinion on this.