1. Chop down the boards in the PaP area with the axe.
2. Shoot the generator in the Pre-PaP area with the Prototype weapon from the PaP area.
2. Shoot four elevator parts within the map with the Prototype weapon (parts are located in spawn, under the pyramid, and two more in the PaP area).
3. Kill 100 zombies under the pyramid.
4. Power the elevator by the generator under the pyramid.
5. You now have permanent perks even if you go down. Wait for the elevator to come back up and this is where the buyable ending is. The 10 point Pack-a-Punch machine also opens at spawn. Purchase the 93,500 buyable ending to complete the map.

Here's a video guide: https://youtu.be/S50G0ANAJNY