The following Boosters can be unlocked by attaining the levels below. After they are unlocked you may purchase them in the Multiplayer Store.
Point and Shoot (Booster Slot 1) - Reach Level 2, then purchase for $2,000
Bandoleer (Booster Slot 2) - Reach Level 4, then purchase for $2,000
From the Hip (Booster Slot 1) - Reach Level 6, then purchase for $5,000
Scavenger (Booster Slot 2) - Reach Level 8, then purchase for $8,250
Break Up (Booster Slot 1) - Reach Level 10, then purchase for $11,250
Keep Firing (Booster Slot 2) - Reach Level 12, then purchase for $14,250
Down the Irons (Booster Slot 1) - Reach Level 14, then purchase for $18,750
Fleet Foot (Booster Slot 2) - Reach Level 16, then purchase for $23,250
Hell Blazer (Booster Slot 1) - Reach Level 18, then purchase for $27,750
Explosive Expert (Booster Slot 2) - Reach Level 20, then purchase for $32,250
Turtle (Booster Slot 1) - Reach Level 22, then purchase for $40,500
Treasure Bearer (Booster Slot 2) - Reach Level 24, then purchase for $43,500
Sure Foot (Booster Slot 2) - Reach Level 26, then purchase for $52,500
Launch Man (Booster Slot 2) - Reach Level 28, then purchase for $58,500
Sure Shot (Booster Slot 1) - Reach Level 30, then purchase for $64,500
Monkey Man (Booster Slot 2) - Reach Level 32, then purchase for $72,000
Walk Softly (Booster Slot 1) - Reach Level 34, then purchase for $79,500
Scoped In (Booster Slot 2) - Reach Level 36, then purchase for $87,000
Juggler (Booster Slot 1) - Reach Level 38, then purchase for $94,500
Deposit (Booster Slot 2) - Reach Level 40, then purchase for $98,250
Rapid Hands (Booster Slot 1) - Reach Level 42, then purchase for $111,000
Rocket Man (Booster Slot 2) - Reach Level 44, then purchase for $120,000
Situational Awareness (Booster Slot 1) - Reach Level 46, then purchase for $129,000
Revenge (Booster Slot 2) - Reach Level 48, then purchase for $134,250
Evasion (Booster Slot 1) - Reach Level 50, then purchase for $210,000
Veiled (Booster Slot 1) - Reach Level 51, then purchase for $300,000
Invalid (Booster Slot 1) - Reach Level 52, then purchase for $350,000
Half Loaded (Booster Slot 2) - Reach Level 54, then purchase for $400,000
Glass Jaw (Booster Slot 1) - Reach Level 56, then purchase for $1,500,000
Come Get Some (Booster Slot 2) - Reach Level 58, then purchase for $2,000,000