Save your Money
While doing the campaign mode for the first time purchase the AUG and upgrade this most of the way, as this weapon has high damage and accuracy.
Then for the sniper rifle purchase the SVD.
Save your money and don't bother purchasing any other weapons as when you pass it you will unlock all the primary weapons. Then when you pass it on Professional you will unlock all the weapons.
This way you can upgrade the weapons you have and also use the extra cash to unlock the Mask (purchase all Masks) achievement.
Added by: deadlysnips Apr 11th 2008, ID#2403