Thanks for the replies.
There seems to be a few different ideas regarding a minimum fee.
1. There is a real cost to opening a job file, covering your one-hour job with insurance, paying the phone bill and typing an invoice.
2. There can be some real benefits to "helping" someone for free. It's good advertising. You'd have to pay for regular advertising. Giving someone a free hour costs you nothing except for the lost income.
I guess it's each case according to its merits.
RDK, I think your suggestion of $100.00 minimum is fair and even.