Buy only what you need.
A simply solution would be...
Buying a L96, as you stated you like using.
Then not buying any modifications for your M16, as this saves you a good amount of GP.
Just kill someone, and take their weapon, and go from weapon to weapon.
Stay away from helmets and armor and such.
Helmets don't help, as regardless of the stated information that supposedly gives you a protection, a headshot whilst wearing a helmet is still a one shot kill.
Play OMA (On Man Army) as they are fast, and give a decent amount of GP as well as XP.
Those are some ideas, post back if you'd like more examples.