14 cards where the mana cost is greater than or equal to {X} and the card types include “artifact” and the color identity ≤ R

Walking Ballista (Double Masters #306)
Astral Cornucopia (Commander Anthology Volume II #172)
Stonecoil Serpent (Commander Masters #976)
Hangarback Walker (Commander Masters #951)
Clown Car (Unfinity #186)
Chalice of the Void (Masters 25 #222)
Orochi Hatchery (Commander 2015 #260)
Engineered Explosives (Double Masters #252)
Shifting Wall (Stronghold #140)
Sigil of Distinction (Shards of Alara #219)
Briber's Purse (Khans of Tarkir #217)
Chimeric Mass (Modern Masters 2015 #204)
Phyrexian Marauder (Visions #151)
Riptide Replicator (Onslaught #309)

This search is finished. Now the real work can begin.