AIM is free. I think you are mixing up AOL with AOL IM. (AIM)
AOL is the connection software to the net. Best advice is to ditch it and go to another one. AOL (also known as A O HELL) is not stable with Windows, and is the most cause of computer problems. I suggest Earthlink, they are the only ISP (internet provider) that has not given me any hassles at all.
AOL Instant Messenger (AIM) is just a messenging tool, like Windows Messenger, ICQ etc. AIM Express is just a lite version of AIM.