You can currently get a mythic rare borderless Vivi Ornitier card for less than $300, though there are some better (and cheaper) legendary creatures to build a commander deck around
They run enough creatures so that the front side is closer to a Spirited Companion than youd think, and the backside is just great

Brago, King Eternal Ultimate Masters Guilds of Ravnica Niv Mizzet, Parun, Emmara, Soul of the Accord, Lazav, the Multifarious (decklist in the comments), Tajic, Legions Edge, Etrata, the Silencer, Izoni, Thousand-Eyed Commander 2018 Aminatou, the Fateshifter, Xantcha, Sleeper Agent, Lord Windgrace, Brudiclad, Telchor Engineer Core Set 2019 Sai, Master Thopterist, Goreclaw, Terror of Qal Sisma, Vaevictis Asmadi, the Dire, Chromium, the Mutable Battlebond Dominaria Teshar, Ancestors Apostle, Grand Warlord Radha, Arvad the Cursed, Muldrotha, the Grave Tide, Slimefoot, the Stowaway, Yargle, Glutton of Urborg, Squee, the Immortal, Firesong and Sunspeaker, Jodah, Archmage Eternal, Tiana, Ships Caretaker Masters 25 Rivals of Ixalan Azor, the Lawbringer, Etali, Primal Storm, Nezahal, Primal Tide, Zacama, Primal Calamity, Tetzimoc, Primal Death, Zetalpa, Primal Dawn, Ghalta, Primal Hunger Unstable Grusilda, Monster Masher, Dr

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