If you buy a dropped domain from Snap or Namejet, the backlinks seem to be worthless for SEO.  They are valuable for traffic if it's targeted to your site.  Go ahead and 301 redirect into your site because it's the traffic from the back links that is worth something.  I use the Google URL builder to redirect these names so you can see the domain the traffic is coming from.
I have some pot related ones I've purchased recently that deal with the manufacturing of hemp like hempmfr.com, hempmoulding.com, hemp-textiles.com, hempecofuel.com etc.  Some of the older domains I've been sitting on are ones like internetpot.com, califunk.com, cafunk.com, caedibles.com, 1tokewonder.com, govherb.com, grasspeddlers.com, pot-megastore.com, usgov420.com etc.  Another interesting recent on I've purchased is Dogparkdates.com and dogpark-dating.com. Do any of these seem valuable in your eyes?
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.