The second option requires a bit more time and effort than a 301 redirect. You could do a mini overhaul of the site and turn it into a microsite for your main domain. This option is good for exact-match domains for your targeted keyword, and there are other reasons for going the microsite route that Rand's highlighted in his post about root domains, subdomains, subfolders and microsites. This strategy also works better if the old domain has decent rankings for the keywords you're targeting.
Determine your domain's value. Before you start taking offers or listing your domain, take stock of its value so that you can come up with a good price. There are a lot factors to take into consideration when determining the value of a domain, so if you are unsure it may be wise to contact a company that performs these assessments. Some of the major factors include:
What I like to do is sort by DP which stands for domain pop, and this is basically the number of linking root domains. So, BL is the number of back links. As you know that can be somewhat misleading if they have a lot of site wide links or multiple links from the same domain. I like to sort by domain pop. What that does is it brings up the sites with the most amount of referring 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.