Skeat, that sounds close. Around here quilters charge between .0125 - .015 per inch; thread (especially variegated or specialty thread), batting, and sewing on the binding are all extra.
Most will provide a price listing to help you figure out how much a particular quilt will cost, and it should list out any charges that are extras. A twin size is generally 60" x 90", but you should always measure the one you're sending so that you get a good idea ahead of time how much it will cost.
Don't let one experience guide you; if she is much higher or charges a lot of extras, you may find someone else who doesn't :wink: