Yes, just like everything else, buying in ‘bulk’ usually means you get a discount.
I have found over the years that my time and creativity is usually best utilized all at once. I put a lot of research and thought into designing your branding which not only includes your logo, but fonts colours and all possible future applications. (For example; business cards, website, ads, signage, packaging, marketing and promotional material etc.) These are all the different variables that I think about to help determine the end design. So, when I am already in ‘research/brainstorming mode’, it’s much faster, efficient and easier for me to move from, and between, one item to the next. Less time, means less money for you.
That said, this is not to say that I can’t or won’t help you with future related design projects. Of course I will. If a logo is all you need for now, that’s great. (See next question) It just means that, later on, I might have to re-familiarize myself with your branding and get myself back into that frame of mind, and do some new brainstorming. Therefore the job will take a little longer than if I had done while it was in the groove of things.