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.