If you have a map which you have made on forge and have run out of money then delete a SMG or Spiker or Plasma Pistol.
Once you have deleted one of the above replace it with a gravity hammer then waste the ammo on it and go back into forge mode and despite having no money you will still be able to put in various weapons and items (the weapons/objects vary).
Please note: this cheat has only been tested on Vallhalla and Sandtrap so if it does not work on any map please let me know.