I need to buy a recorder, something cheap, so that I can record a conversation.

I received a bad grade on an assignment I did for a professor who absolutely hates me. I plan on meeting with her to discuss the failing grade she gave me and to discuss the unprofessional remarks she made. I need this recorder in case I need to take this situation to the college dean. Can anyone recommend a purse-sized voice recorder so that I can successful record the conversation we’ll have when I meet with her? I am close to a radio shack and walmart. I’d prefer something cheap (maximum of $30) and subtle. Oh, and if it has a USB, so that I can upload the conversation to my laptop, I’d really like that, too! Please help. Thanks.