Some of the lesser known agencies are located off airport property and not at the McCaren rental center. Yes most do have a shuttle but it takes longer and you may have to shuttle to the rental center and then transfer to one of their shuttles.

Rental rates have been fairly low till about a week ago and then they took a jump. Try using Travelocity or Kayak to find low rates. The sites keep saying cars will be in short supply for convention week. I booked for 5 days a while back for close to $100 total at Advantage. I consider that a good rate.