The Artifact is popular within the MTG Commander format, and its highest-priced version is from Invasion at around $400
Dont sleep on Author of Shadows, either sure its a ten mana combo, but exiling an opponents Teferis Protection or Heroic Intervention can help you close the game
These are the first cards I'd recommend removing to make room for upgrades: Compleation on a Budget Here's a list of $5 or less upgrade options for Breed Lethality to give you ideas on where to take the deck
There are traditional combat damage payoffs like Cranial Plating, Kappa Cannoneer and Nettlecyst, and some powerful non-combat threats like Ghirapur Aether Grid or Mechanized Production
For each game after the first, the loser of the previous gets to choose who goes first without a coin flip Draw 7 cards for your starting hand
Popular general enablers include cards like Enlightened Tutor, Mox Opal, and Elvish Mystic