This will come most probably without noticing.
What i was doing to get this achievement and not to waste money that i needed for later on, was on every mission i was buying the intel pack (2500cp) for the map to be revealed! On the 10th level i had the achievement.
You may get it earlier, especially if you are ordering medic packs or grenades.
A hint: Always get and kill everything in every map, so you get more money to help you buy things easier and without a struggle.
Good luck :)