I mainly use the site
https://www.expireddomains.net
The price of domains varies widely. You need to purchase the most effective domain according to your competitors' situations and your budget.
When buying a domain, the first thing to check is whether the domain is still indexed by Google. Also, use the Wayback Machine to check what the site was previously.
If the site was spammy or part of a PBN, you could receive a penalty even after rebuilding it. Tools like Archivarix can be used to download and utilize the content.
The most important step is to check the backlinks of the domain using tools like Ahrefs.
Verify the topic of the previous site and the types of backlinks it had. Also, check the anchor text to ensure there are no spammy backlinks.
When checking backlinks, identify which pages need to be rebuilt. Determine which pages had the most backlinks and use tools like the Wayback Machine to revive those pages.
This is the basic procedure, but it requires many additional tasks. If you don’t have much experience with domain rebuilding,
I don’t recommend it. I’ve seen many cases where the cost of buying the domain is wasted due to incorrect reconstruction.
If the scale of the competitor's site isn't very large, I would use the budget for purchasing a domain to develop an alternative SEO strategy instead of domain rebuilding.