As with anything, it really depends on what elements of digital marketing you’re looking to add to your strategy.
If you’re focusing on inbound techniques like SEO, social media, and content creation for a preexisting website, the good news is you don’t need very much budget at all. With inbound marketing, the main focus is on creating high quality content that your audience will want to consume, which unless you’re planning to outsource the work, the only investment you’ll need is your time.
With outbound techniques like online advertising and purchasing email lists, there is undoubtedly some expense. What it costs comes down to what kind of visibility you want to receive as a result of the advertising.
For example, to implement PPC using Google AdWords, you’ll bid against other companies in your industry to appear at the top of Google’s search results for keywords associated with your business. Depending on the competitiveness of the keyword, this can be reasonably affordable, or extremely expensive.