The Lathril precon is $20, this is a $50 upgrade at TCGPlayer. These upgrades are to add as much competitiveness as possible for $50.

• Combo cards to untap Lathril and Archdruid/Marwyn/Channeler (Staff of Domination).
• Mana sink win conditions to use infinite mana with (Elvish Warmaster, Leyline of Abundance).
• Elf combo to make Lathril huge (Immaculate Magistrate + Copperhorn Scout).
• More one drop mana Elves to cut some lands (Elves of Deep Shadow, Fyndhorn Elves, Llanowar Elves).
• Creature tutors (Chord of Calling, Wirewood Herald, Pyre of Heroes).
• Some more Golgari dual lands that can ETB untapped (Llanowar Wastes, Unclaimed Territory, Tainted Wood).
• Untappers to use Elves who have a tap ability more than once a turn (Copperhorn Scout, Wirewood Symbiote) .
• More evasion for Lathril and Elf tokens since menace is not quite enough to consistently do combat damage to a player (Champion of Lambholt, Vorrac Battlehorns, Fallen Ideal).
• More mass draw with Elf tokens (Shamanic Revelation, Regal Force).
• Better reanimation (Haunting Voyage, Victimize).
• Opponent sided board wipes (In Garruk's Wake, Crippling Fear).

41 cards to cut from the precon:

• 7x Swamp
• 2x Forest
• Foul Orchard
• Golgari Guildgate
• Roots of Wisdom
• Harvest Season
• Ambition's Cost
• Eyeblight Massacre
• Return Upon the Tide
• Tergrid's Shadow
• Casualties of War
• Serpent's Soul-Jar
• Binding the Old Gods
• Pride of the Perfect
• Moldervine Reclamation
• Masked Admirers
• Voice of the Woods
• Twinblade Assassins
• Eyeblight Cullers
• Cultivator of Blades
• Voice of Many
• Rhys the Exiled
• Lys Alana Scarblade
• Elvish Rejuvenator
• Jaspera Sentinel
• Llanowar Tribe
• Harald, King of Skemfar
• Lys Alana Huntmaster
• Crown of Skemfar
• Jagged-Scar Archers
• Sylvan Messenger
• Farhaven Elf
• Springbloom Druid
• Prowess of the Fair

New precon deck list with $50 upgrade: