Skip the $20+ cards (Thrumming Stone, Coat of Arms, Cover of Darkness) and the deck still hums: Commander: Karumonix, the Rat King (~$1) Engines: Pack Rat (~$3.30), Piper of the Swarm (~$3), Ogre Slumlord (~$0.45), a couple of Relentless Rats / Rat Colony (~$56 each cap the copies to stay on budget) Payoffs/utility: Crypt Rats (~$0.50), Nezumi Bone-Reader (~$0.40), Bontu the Glorified (~$3) as a sac outlet, Throne of the God-Pharaoh only if budget allows The rest: cheap black removal, Swamps, and a Sol Ring The whole list comes in well under $50, and it scales up gracefully add Marrow-Gnawer and Thrumming Stone later and the same shell jumps several power levels
This can give you a solid burst of mana, and its great for trying to pull ahead of the table
I mentioned earlier that this deck had some pretty weird cards in it
5 Nuka-Cola Vending Machine (Borderless, Surge Foil) Who Doesn't Enjoy An Ice-Cold Nuka-Cola
Ulamog, the Defiler (Retro Foil) $76.99 Most Eldrazi titans create prohibitive board states and totally flip the advantage, even if most of these cards have high mana costs