The total amount of loot in the level is 97.370, use the fully upgraded magnet gadget.
This is the amount of loot you should have at each checkpoint, this includes the loot that is directly AT the checkpoint:
-Start : 0
-Checkpoint 1: 630
-Checkpoint 2: 630
-Checkpoint 3: 1710
-Checkpoint 4: 1710
-Checkpoint 5: 3330
-Checkpoint 6: 5490
-Checkpoint 7: 7990 (when at this one the 2nd time, after the 1st skull location)
-Checkpoint 8: 10780
-Checkpoint 9: 14020
-Checkpoint 10: 17800
-Checkpoint 11: 20300 (when at this one the 2nd time, after the 2nd skull location)
-Checkpoint 12: 24620
-Checkpoint 13: 29480
-Checkpoint 14: 34880
-Checkpoint 15: 60570 (before getting the 4 purple gems on the 2nd wheel)
-Checkpoint 16: 72510
-Checkpoint 17: 80950 (when at this one the 2nd time, after the 3rd skull location)
Note that at the 14th or 15th checkpoint emenies start attacking you and try to take your loot. What i did for this section is stand on top of the chariot or right next to it (find the right angle to hit the centre of the chariot) and keep spamming the attack button so everything that touches the chariot dies, if you do this quickly you have a few seconds to move on before the next wave arives, rinse and repeat this. Ofcourse you could always log in a 2nd player with the special attack equipped to make it easier, i think the achievement was designed with that in mind.
Alternative method : For checkpoint 15, when you're collecting purple gems from the first big wheel, you can return to the checkpoint and retrigger it after each gem. Reload the checkpoint, and all the looters will have calmed down so you can collect the next gem in peace. A lot easier than doing them all in one go. ( credit goes to: RazorPriest )
If theres anything i should add or change plz let me know.