But what kind of information should you gather for your own buyer persona(s) to inform your digital marketing strategy? That depends on your businesses, and is likely to vary depending on whether you're B2B or B2C, or whether your product is high cost or low cost. Here are some starting points, but you'll want to fine-tune them, depending on your particular business.
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.
Unlike most offline marketing efforts, digital marketing allows marketers to see accurate results in real time. If you've ever put an advert in a newspaper, you'll know how difficult it is to estimate how many people actually flipped to that page and paid attention to your ad. There's no surefire way to know if that ad was responsible for any sales at all.
AdWords is an excellent way to display your products or services on Google's results pages for very specific queries. For instance, let's say someone searches for "best CrossFit gym in Austin". Sure, you could work on your SEO and hope to appear organically -- but you can also bid on the keyword and appear at the top of the page, enabling you to capture tons of high intent visitors.