Actually, with the internet coupons, the off-airport parking places are cheaper than the long-term parking lots and significantly cheaper than the daily garage. Econopark Express and Airport Fast Park are under $7/day. The BWI economy lots are $8/day and daily garage is $10.

Given the off-airport lots' speed of pickup and better customer service, I now consider anyone that parks anywhere else crazy (except if they're doing what I've done a few times, which is to park in the hourly garage and run for their flight because he is so late that any other option would mean DEFINITELY missing the flight! )