In the late 90s, a work colleague/friend of mine was putting on fund raising concert events to finance the 2000 Llanelli Eisteddfod. A little known local singer was booked well in advance for one of these events. I'm not sure if there was any fee, but if so it would have been minimal. By the time that the concert was to take place, she had become well known.
I still remember my friend telling me how impressed he was, when Shan contacted him to mention that she was keeping her diary free so that she could honour the booking.