Listen to expert domainers on domainsherpa.com. Read anything by Michael Berkens, Frank Schilling, Eliot Silver, Morgan Linton, and Ron Jackson. Watch YouTube videos on domain investing. Read blogs like The Industry News Magazine at DNJournal.com. Search #domains on Twitter. Go to industry conferences. Understand the Google Keyword Planner tool inside and out.
Hundreds of thousands of domains expire everyday. While most of them are trash, quite a few are aged domains having excellent backlinks. These can be easily filtered using metrics from Majestic (Trust Flow) & Moz (Domain Authority). These are great for your money sites or for building private blog networks. Some of these domains have natural organic traffic, that can be determined by their SEMrush rank or the SimilarWeb data. These are great for domain parking or for promoting affiliate offers.
That said, my recommended budget for beginners would be $500+. Using this budget you could buy a bunch of high-potential $10 domain names, expired/dropped domain names or a mix of both. It’s very important to invest only what you can afford to lose and treat this as a side hustle till you get the momentum going. As you gain experience, industry expertise and some sales under your belt, you can then consider slowly growing your business into a full-time gig.