The Comfort Inn in Memphis has a crew rate of about 50 bucks a night and I'm pretty sure a shuttle back and forth to and from the airport. Their number is 901-345-3344. I never stayed there, but some other people in my class did and they didn't make it seem too bad. I was based there for a month on my green line and only once did I have to find a place to stay. Otherwise it was very commutable (departing MSP). So if the majority of the month is trips on your green line I'd definitely recommend not spending money on a pad. If you still think you really need a crashpad, there are a couple of guys with them down there, pretty sure you'll need a car at any of them though. Good luck!