The magic number of Internet versus traditional advertising doesn’t really exist in businesses. However, if you really want to monitor the ROI of all of your marketing channels use the Google Analytics tool, it should be easy to see which marketing methods are the most effective.
If you eliminate the methods that don’t bring results, you’ll have more money to spend on the ones that are effective. As a result, you won’t actually need to spend any more than you already do on digital marketing- you’ll have to just adjust it.