If domains are real estate, then the same rules of real estate should apply. In real estate, taxes are based on the value of the property. So, a person asking $10,000 for a domain shouldn't be paying the standard $15-30 renewal fee as a person asking $200. The renewal fee should be based on the domain's value. Domainers want to claim it's like real estate without applying the most fundamental rules of real estate.
A rule of thumb that I follow is when I purchase a domain name I have to believe that I can flip it for a 100% profit. So if I spend $500 on a domain I need to feel like I can sell it for no less than $1,000. This way, even if I’m wrong in my estimation I still have some room to still turn a profit. And if worse case comes to worse case I’ve sold domains before for a $0 profit (it happens even to the best of us).
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.