@ib2 @T-3D I've been a domain investor for over 10 years and have been very successful at it. There's a lot more that goes into it then just registering a domain name and hoping it will sell. You can list your domains on Godaddy auction listings or on premium listings, I've had a lot of success with those. Some good resources are namebio.com, dnjournal.com, namepros.com and others.
Use the advanced search option to quickly hone in on the type of names you are interested in. You can narrow the results by price, top-level domain (i.e, .com, .net, .org, .club, etc.), keyword, and many more filters. Using this feature will help you quickly sort through the millions of domains on the aftermarket and find the domain names that best fit your end goals.
If you know how to get websites to page one, why are you not marketing that fact to potential clients and consumers or would-be domain purchasers? Trying to get a keyword driven domain to rank high and sell it off for a profit isn't a good investment, either time wise or for the long-term success of your company. Instead, use sites that you have already ranked high as an example of how awesome you are and sign them up for a monthly fee, rather than trying to sell them a "make money now" domain.
Get appraisals for your domain names. When selling, you will want to know what kind of price you should expect to get for your sites. There are a variety of websites that offer free appraisals for valuation. This includes larger domain auction sites such as Sedo.com, GoDaddy.com, and DomainIndex.com. These of course are only estimates, but they can give you a good idea of what certain domains might be worth.
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.