This works best with 2 players:
1. On round 1, shoot each zombie ~7 times with the M1911, then knife it. Don't get any headshots. You should have enough money to open at least the 1st door, and the 2nd person might have enough for the 2nd door.
2. Shoot each zombie up to ~12 times, then knife it. Open the 2nd door if it hasn't been done yet, then the 3rd door.
3. You are probably out of ammo by now, but may have gotten a Max Ammo. If you still have ammo, you can shoot a zombie up to ~17 times, then knife it. By the end of the middle you should be on the Stage. Hopefully you have stumbled upon a mystery box by now. Buy a weapon from it when you are close to running out of ammo in your pistol. Do not turn on the power. If you do, Creepy Crawlers will start coming, which you don't want.
4. If you still have ammo, shoot a zombie up to ~22 times with the M1911, then knife it for maximum money. Start earning money for the Pack-a-Punch. still leave the power off.
5. You should have enough to PaP sometime during the round. As soon as you do, turn on the power, link it, and Pap whatever you have, be it M1911 or Mystery Weapon.