It depends upon what you’re looking for.
You’re conflating several different things.

1 - United Club access. You can purchase United Club access, or get it included as a perk of the Chase United Club credit card. United Club members are also allowed access to *A business class lounges in airports where they exist.
2 - United Gold status. United Gold status includes Star Alliance Gold status, but does not include lounge access on domestic itineraries unless you are also a United Club member. It does include lounge access on international itineraries. It also includes Economy Plus seating for you and one companion at the time of booking (if E+ seats are available) and theoretically includes complimentary upgrades to domestic first class on eligible routes. However, the upgrade clearance rate for Untied Gold members tends to be extremely low, especially if they live in a United hub city. Premium transcontinental routes such as SFO/EWR and long-haul international routes (TATL, TPAC, Hawaii except to/from California) are excluded.
3 - Star Alliance Gold status earned through another program. This gets you access to the United Club on all itineraries, international or domestic, but does not include Economy Plus seating or the possibility of upgrades.

The choice between these really depends upon which particular benefits are important to you.

Each of these would require annual renewal unless you achieve lifetime status with United, which requires flying one million miles on an airline you don’t like.

You’re getting conflicting / unclear answers because you’ve asked about several different topics and people are trying to be helpful. For the purposes of clarity: You cannot buy United status. The United PassPlus program, that some people have mentioned as offering status for $25,000 or $50,000, is a pre-paid travel program designed for businesses. If you wanted to commit to that level of purchases (again, with an airline you don’t like and don’t want to fly), they will give you status for the program year.

Airlines aren’t stupid, and they’re not particularly interested in offering a subscription of benefits at low cost to allow for their customers to maximize value. You appear to be looking for a way to spend a small amount of money and get all of the benefits of a large customer — and wouldn’t we all like that? But UA has systematically closed those loopholes.