Grab yourself a Sniper for long-range, Sub Machine Gun for close range, Assault rifle for a good balance, or a Light Machine Gun for max ammo.
All Primary Weapons cost 2000 Points after reaching the unlock level or purchase threshold. All weapons unlocked by default require 0 points.
Assault Rifles

M16
Unlocked: Default

Enfield
Unlocked: Level 5

M14
Unlocked: Level 9

Famas
Unlocked: Level 14

Galil
Unlocked: Level 20

AUG
Unlocked: Level 26

FN FAL
Unlocked: Level 32

AK47
Unlocked: Level 38

Commando
Unlocked: Level 44

G11
Unlocked: After buying all other Assault Rifles.
Submachine Guns

MP5K
Unlocked: Default

Skorpion
Unlocked: Level 7

Mac11
Unlocked: Level 11

AK74u
Unlocked: Level 17

Uzi
Unlocked: Level 23

PM63
Unlocked: Level 29

MPL
Unlocked: Level 35

Spectre
Unlocked: Level 41

Kiparis
Unlocked: After buying all other Submachine Guns
Shotguns

Olympia
Unlocked: Default

Stakeout
Unlocked: Level 8

SPAS-12
Unlocked: Level 24

HS10
Unlocked: After buying all other Shotguns
Light Machine Guns

HK21
Unlocked: Default

RPK
Unlocked: Level 6

M60
Unlocked: Level 21

Stoner63
Unlocked: After buying all other Light Machine Guns
Sniper Rifles

Dragunov
Unlocked: Default

WA2000
Unlocked: Level 10

L96A1
Unlocked: Level 27

PSG1
Unlocked: After buying all other Sniper Rifles