Good point. Is the amount of work that went into getting a successful sale worth a $400 profit? Keep in mind, this is providing speculative numbers for the sake of debate. The real world hours invested in gaining position or page rank, and time a agency would sit on a domain before a sale would be much higher. We interviewed a few agencies that practiced this, not only those that supported our theory.
Something wise my father once told me "Something is only worth how much someone is willing to pay for it." This small seemingly unimportant statement has guided me in many selling and purchasing decisions in my life. Sometimes, it makes the reality all too apparent. So, is buying a domain with the intention of selling it a good idea? Let's break down the details, and talk to some people that actively pursue this method. Yeah, we know a guy.
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.