Re: Costs to entire projects
You cannot assign resources (material or work) to the project summary task. You can assign cost budget resources, but that is at a flat rate.
An option is to create a hammock task and then assign a material resource at a variable rate per day.
See below for the information on hammock tasks:
http://support.microsoft.com/kb/141733/en-us
Although the article references Project 2003 - it still works the same in 2013.
The create the material resource and set its rate to $1.00 per hour. As you assign the resource enter your estimated usage per day in the units field. For example 100/d would apply $100 per day to the task. If the task duration grew or shortened, the cost would grow or decrease as desired.