The Shackled Ur'zul is a very rare drop from Argus the Unmaker, the final boss of Antorus, the Burning Throne, on Mythic difficulty. This mount can be purchased through the Black Market Auction House.
Here you can buy Shackled Ur'zul for EU or US Servers.
You'll get guide for getting Shackled Ur'zul
You'll be able to get Shackled Ur'zul
Additional budget for Character transfer or Character boost to max level. BMAH Services in Shadowlands now requirement to have a max level character on server, so Trial character will not work.
Free time on evening, if you choose selfplay option