Question

If you could borrow all the money you need for a project at 6.5%, does that mean that the cost of capital for this project is going to be 6.5%?

Answer 1

No, that does not mean that the cost of capital for this project is going to be 6.5%
In business, cost of capital means the total value lost when you decided to choose a certain investment over another.
In order to calculate it, you need to consider other factors beside interest rates, such as your equity to debt ratio and your tax rate