What a validation of your skills! Charge travel expenses (mileage/gas) and ask to be taken to lunch with guild members before your afternoon class; then charge what you are comfortable with, maybe $50-75 if this is your first such experience. Be sure to show some of your quilts -- everybody loves a trunk show!
Do you know what this guild usually pays their speakers, or can you ask? Try not to undersell yourself.
Jan in VA