The following number of orbs are required to upgrade the indicated weapon.

Blades Of Exile
Level 1: 0
Level 2: 4,000
Level 3: 7,000
Level 4: 8,000
Level 5: 10,000

Bow Of Apollo
Level 1: 0
Level 2: 2,500

Claws Of Hades
Level 1: 0
Level 2: 3,000
Level 3: 5,000
Level 4: 6,000
Level 5: 9,000

Head Of Helios
Level 1: 0
Level 2: 2,500

Boots Of Hermes
Level 1: 0
Level 2: 2,500

Nemean Cestus
Level 1: 0
Level 2: 3,000
Level 3: 5,000
Level 4: 5,000
Level 5: 8,000

Nemesis Whip
Level 1: 0
Level 2: 3,000
Level 3: 5,000
Level 4: 5,000
Level 5: 8,000