Transmute Artifact

Sacrifice an artifact. If you do, search your library for an artifact card. If that card's
mana value is less than or equal to the sacrificed artifact's mana value, put it onto
the battlefield. If it's greater, you may pay {x}, where X is the difference. If you do, put
it onto the battlefield. If you don't, put it
into its owner's graveyard. Then shuffle.