Also with the domains, a name which can be cheap for one can be worth gold for the other. Permute the letters in your domain name and try contacting and eventually selling out to organizations that run under those names or contain the letters within. Companies would be keenly interested in buying out the domain names that matches the product's name. Hint : Look for companies on LinkedIn
What about option #4 - Redirect your existing domain to the old domain? I bought an old domain that is 100% relevant to my current domain but currently has with very little content. It did have more content fours years ago. The old domain is 13 years old, pr=3, while my current is 7 months old pr=1 and a decent amount of content. The old domain I purchased was not expired though and I do not know if this makes a difference. What are the pros and cons of option #4? Am I correct to think that option #1 would result in no benefit from the old domain's age value and if so why is it not listed as a con, a MAJOR one. Its hard to believe that a 301 using option 1 would give my existing domain 13 years credit but I'll take it if it does.
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.