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.

I've seen some people comment about losing the link value of domains that have expired and picked up, but what about non-expired domains?  Let's say a competitor is going out of business and they still have a year or two left, and we buy their domain and site.  Is there a risk changing registrant info and registrars, even if I keep their site up and mostly the same as before?  I was under the impression that I'd want to keep it under their name so as not to hit the uber-reset button on the domain's inbound link value.

For the following TLDs you can now find a expired/deleted domain list. .cr, .gd, .gs, .im, .ke /, .kg, .kz, .ir, .la, .ma, .pe /, .pm, .re, .tf, .wf, .yt, .so, .th /, .uz They also show up in the Deleted Domains (last 7 days) list and in the Domain Name Search, however they are not in the pending delete list! I do not have a working droplist for them yet, so that is why they are not released in the pending delete list yet.
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.