I'm not sure exactly how the trading works, but the prices you mentioned are pretty much accurate based on what I've heard, I'm actually from the Philippines, and majority of the artists here have their accounts verified and entitled to have a vanity username. Years ago, the username
@james is being auctioned by someone, though the profile looks inactive and dead, no posts, not even a profile photo, it just hold the username, so many people bid, they said even social media managers of Lebron James wants to get that username and willing to pay as much just to get it, the price reached around 200k PHP here in the philippines, around 4k USD and the bid goes on and on, until the account has been gone. Some hackers even try to hack the account, but it has been deactivated and wasn't able to reach around the radar for almost a month. Moments past, a lot of personalities around the globe wanted to have the vanity username. But it was claimed by James Reid, a filipino artist. I'm surprised, as lebron himself can probably pay based on his net worth, and James Reid here didn't even pay for it, but the management he is signed to, got it free for him, haha majority of the artists here, well known or even not as long as they are signed with a proper management got their profiles verified and have their vanity username, usually their first name, which also boosts their overall SEO performance when someone search for anyone having the same name.
I've talked to someone local here who is a guitarist in a filipino band(not so mainstream, their IG only have 30k followers) and all of them members of the band have been verified and have their vanity username even though they average from 900+ to 2.5k followers per member account. I'm in a band too(but an indie) so I was able to talked to this person, I've got 20k+ followers on my personal account, and wasn't been able to get verified, I claimed my vanity username in the hardest way possible. But he said, everything has been done for free by their record label. Damn, I'm really jealous. The band I belong don't have any record label yet, and we aren't signed up to any management and that is probably not going to happen as we all the members are all professional in different fields. But I'm pretty sure some people here in the entertainment industry have connection to facebook and instagram as they are able to do that kind of thing. The man who told me that is a friend, he doesn't have any wiki page or any publications, got 900+ followers, and didn't submit any documents such as IDs, everything has been done for free as part of their contract. Some people out there can claim any username they want.
Try to read this story, he's not been hacked, instagram gave his username to a football player. Spoiler, he regain it back though after his story became viral.
https://medium.com/@ainiesta/how-in...-gave-it-to-a-football-celebrity-625a6a770eb3