We (four adults in two rooms) are heading to Boston for three nights beginning September 7. We are mainly interested in historical sites. How close to that date can we safely hold off booking rooms? Since this is right after Labor Day, would it be easier or harder to find available rooms below $150? I'd love to get a deal thru Hotwire, but frankly, it scares me to book a month in advance since it's not refundable.