Price it out, you might be able to get a cheaper made cable from a company like CDW. You could also have a local computer/networking store create one for you.
Cat5e can handle weather conditions, especially in your attic. Generally, if you don't have access to the cable and it is through a wall or not in the open, you will need to use plenum. That would be to code but since it is only a single cable, I would save the money and use a regular cable. The poisonous gas emitted when burning is only dangerous if you have a lot of it burning and you're inhaling a lot of it.
Based on that one cable, the smoke will get you first if you decided to stay in your house.