We paid the $12 a day for the 8 day voyage on the Star...was $96. Be careful as the lot charges $12 for the next 24 hours (or any portion thereof) if you go over into the next 24 hour period. We ended coming back with 20 minutes to spare before etting charged, but waited 25 minutes in line to pay. Told the booth attendant that we would not pay the next $12 due to waiting in line.
You can also find some deals with local hotels where you stay the night before and then leave your car in their lot for the week and get a free shuttle to the pier.