When the instants or sorceries deal combat damage to a player you can copy the card that it is without paying the mana cost
Glimpse of Nature Whenever you cast a creature spell this turn, draw a card Last March of the Ents This spell cant be countered Draw cards equal to the greatest toughness among creatures you control, then put any number of creature cards from your hand onto the battlefield Lifes Legacy As an additional cost to cast this spell, sacrifice a creature Draw cards equal to the sacrificed creatures power Rishkars Expertise Draw cards equal to the greatest power among creatures you control You may cast a spell with mana value 5 or less from your hand without paying its mana cost Budget There are some might fine cards that fall in the budget category of green card draw sorcery spells

There are a bunch of Commander Classics like Hornet Queen, Nantuko Vigilante, Caustic Caterpillar, future strong cards like Haywire Mite, multiplayer classics like flying regenerator Fog of Gnats and the card drawing and recurring Grave-Shell Scarab, token making Ant Queen, game winning rampers like Moldgraf Monstrosity, Giant Adephage and Living Hive
a cheap threat that draws plenty of cards does wonders, even if it means you need to restrict your mana curve