I have visited HBS this year. Don't drive as it is hard to drive in Boston. Take either subway or simply take the cab. Cost about $40 to HBS for cab and <$3 for subway. You need to change different line for subway.
For Hotels, simply bid on priceline because it is expensive to live in Boston. If you can ask someone to share the dorm with you, save a bunch. expect to pay $50-$100 for hotel. I stayed at airport for the first night and then take cab to the city.