Well.. since this post, I have done quite extensive research and have not found any information or a sheet about this. I would appreciate it if you could send me any relevant information as an clickable link(:

Username for bots New
You can now upgrade collectible usernames to assign them to Telegram bots.
To upgrade, assign the username to a bot and pay a one-time fee of 5,000 per username.
Usernames will remain upgraded even if they change owners. More info

10K $ so I can send custom emoji, A lot of money

I saw in the Telegram API documentation that 'Custom emoji entities can only be used by bots that purchased additional usernames on Fragment.' If I purchase a username on Fragment for 20 TON, will I be able to send custom emoji with my bot? Also, where does the 5000 TON price for a username come from if there are cheaper usernames available?

I think that's because in order to assign additional username to a bot you shoud pay extra 1000 TON.