Why advertise online?
Cost comparison of traditional media vs online marketing
Google Adwords = Set a daily budget so you stay within your monthly budget.
Pay per click (from $0.02) means you only pay when users click on your ads.
Louder is NOT better. You want to target only interested customers. Traditional media broadcast messages to a general audience, while Google ads are only shown to people who indicate interest in a particular topic by keying in their search terms.
This makes ads relevant and useful in the same way as natural search results. This is highly effective as you only show your ads to people at the exact time they show interest in your products, hence making the most use of your marketing investment.
With a TV/newspaper ad, you can only estimate/guess the number of interested customers your ads reach. ROI can be measured more accurately if customers need to specify something unique from the ad e.g. code to get the discount, which requires your store staff to measure diligently.
With Google Adwords you can track clicks to your website, number of customers who sent email to you, time on your site (measure interest level) and the online sales from your online ads.
Read on: What is Google Adwords?