There are many places and ways you can purchase domain names.  You can purchase unregistered ones through sites like GoDaddy.  There are forums where people will gladly try to sell you their domain name (usually though the domains being sold in forums are either crap or the asking price is so high it does not allow you any room to flip the domain).  And then there is my favorite way of obtaining domain names, through an online auction at Namejet.  Let’s first talk about Namejet and then we’ll talk about how I personally ring the register by flipping domains.
Those trading domains for commercial purposes are generally on the prowl for lucrative domain endings. There are essentially two different ways traders go about making money off of domain names. One method entails purchasing already established names for a low price and selling them for a profit later once their value has increased. Another strategy involves buying and registering a domain that is thought to possess a high sales potential. Many domain traders use backorder services. These services automatically register a domain when one becomes available or is deleted (what are known as expired domains).

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.