you can use them interchangeably , The only difference is that "perhaps" is used more often in England and it is also considered a little bit more formal than “maybe”.

There's not really a difference I can think of. When answering a request, they mean the same thing. "Perhaps" can be used in other situations, too. http://www.google.com/dictionary?q=perhaps&langpair=en|en&hl=en&sa=X&ei=mJIHTY2jA8SBlAeSgqnHBA&ved=0CBYQmwMoAA

in my opinion 'maybe' is more used colloquially whereas 'perhaps' is used more in written forms like English literature.

Angela is exactly right