In order to complete the Krypt you need about 294,000 koins and unlock 299 treasures but there are 303. If you complete story and challenge ladder you can obtain about 300,000 coins. Also, there are four hidden treasures in the krypt as hinted above. They are...
"In the Deadlands, go to DL52. Between that headstone and the building to the right, you'll see some green bugs moving around on the ground. Back up a little bit. Go to your map, press B. SE1 should pop up. Lightning will hit the ground then claim SE1.
For the one in Hollow of Infestation. Go all the way to the left corner of the map. Then, go to the 6th face on the wall. Press Y to go to the map, then B. SE2 should pop up, the mouth will open and claim your treasure.
For the one in Bloodmarsh. Go all the way to the right corner of the map. Then go to the 5th spot (which would be the 4th face on the wall) Go to your map, press B and SE3 should pop up. The mouth should open, and there's SE3.
For the one in Meadow of Dispair. Go to the stairs of Nekropolis. Staying as far up as the game will let you, go right until you see a group of 4 rocks. About the middle of the stairs and the rocks, again go to your map. Press B and SE4 should pop up. Lightning will hit the ground and then claim your treasure."
If you obtain these treasures, you'll nab yourself 20,000 koins in total and you do not need to buy four treasures as the hidden treasures are counted toward the achievement.
Hidden treasure locations are from "A ZombieTwinkie" on a different forum.