Unexpected Assistance is a common Instant card from Lorwyn Eclipsed (ECL), collector number 80. Current market price: $0.25 (foil $0.31), TCGplayer market prices via Scryfall.
Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.) Draw three cards, then discard a card.