The last rank in reach requires 20 million cr.

Bungie you crazy. Source: kotaku.com
All ranks below:
Recruit
Private - Awarded at 7,500 cR |
Corporal - Awarded at 10,000 cR |
Corporal Grade 1 - Awarded at 15,000 cR |
Sergeant - Awarded at 20,000 cR |
Sergeant Grade 1 - Awarded at 26,250 cR |
Sergeant Grade 2 - Awarded at 32,500 cR
Warrant Officer - Awarded at 45,000 cR
Warrant Officer Grade 1 - Awarded at 78,000 cR
Warrant Officer Grade 2 - Awarded at 111,000 cR
Warrant Officer Grade 3 - Awarded at 144,000 cR
Captain - Awarded at 210,000 cR
Captain Grade 1 - Awarded at 233000 cR
Captain Grade 2 - Awarded at 256,000 cR
Captain Grade 3 - Awarded at 279,000 cR
Major - Awarded at 325,000 cR
Major Grade 1 - Awarded at 350,000 cR
Major Grade 2 - Awarded at 375,000 cR
Major Grade 3 - Awarded at 400,000 cR
Lt. Colonel - Awarded at 450,000 cR
Lt. Colonel Grade 1 - Awarded at 480,000 cR
Lt. Colonel Grade 2 - Awarded at 510,000 cR
Lt. Colonel Grade 3 - Awarded at 540,000 cR
Commander Grade 1 - Awarded at 650,000 cR
Commander Grade 2 - Awarded at 700,000 cR
Commander Grade 3 - Awarded at 750,000
Colonel - Awarded at 850,000 cR
Colonel Grade 1 - Awarded at 960,000 cR
Colonel Grade 2 - Awarded at 1,070,000 cR
Colonel Grade 3 - Awarded at 1,180,000 cR
Brigadier - Awarded at 1,400,000 cR
Brigadier Grade 1 - Awarded at 1,520,000 cR
Brigadier Grade 2 - Awarded at 1,640,000 cR
Brigadier Grade 3 - Awarded at 1,760,000 cR
General - Awarded at 2,000,000 cR
General Grade 1 - Awarded at 2,200,000 cR
General Grade 2 - Awarded at 2,350,000 cR
General Grade 3 - Awarded at 2,500,000 cR
General Grade 4 - Awarded at 2,650,000 cR
Field Marshall - Awarded at 3,000,000 cR
Hero - Awarded at 3,700,000 cR
Legend - Awarded at 4,600,000 cR
Mythic - Awarded at 5,650,000 cR
Noble - Awarded at 7,000,000 cR
Eclipse - Awarded at 8,500,000 cR
Nova - Awarded at 11,000,000 cR
Forerunner - Awarded at 13,000,000 cR
Reclaimer - Awarded at 16,500,000 cR
Inheritor - Awarded at 20,000,000 cR