I believe that it's about $23 a day in central parking. You could use the satellite parking lots. They are under $100 (or in that area). You get a shuttle bus from the lot to your terminal. We did that last summer and it wasn't too bad. Or, you could drive to a hotel, stay the night and have a service take you to Logan then next day. Or there are some hotels nearby that offer free parking and a shuttle if you stay overnight.