My school has required attendance for everything. If you are planning a long commute it would be better if your school did not require lecture attendance and had lecture podcasts. Since my school has a PBL curriculum I'm not on campus all that much, though. The first semester with anatomy had a packed schedule and I had to go in every weekday and most days were fairly long, about 6-7 hours. The second semester was better in that I only had to be on campus 2-3 hours a day, though it was 5 days a week - we had PBL group on Mon, Wed, and Fri and Tues was OMM lecture and lab and Thurs was H&P lecture/lab.
If you were in a more traditional curriculum with lectures all day every day and you had a long commute I could see it possibly interfering with your grades (i.e., if you spent 10 hours a day in class and commuting). I do not feel the long commute has impacted on my grades at all. The problems I had at the start of the year were related to being out of practice as a student and not my commute time. A student in my class told some other students her academic problems were stemming from her one hour commute but IMO that is not a valid excuse at our school.
I not only pay for gas but the only sensible way for me to commute to and from school is on a toll road. I estimate that I pay about $12 in gas and tolls for every day I commute to school. Thinking about this is painful but I haven't had trouble financially, probably because like I said before, you don't have time to do much that costs money during school.