We just went down in March on a last minute cheap flight deal and got in the Comfort Suites for under $200 a night peak season (and they gave an extra 10% off for AAA). The rooms, while not real big, are clean and include a small kitchenettes with micro and frig and offers free wi fi in the rooms and a PC down in the breakfast room. A good continental breakfast is included for free. The Tiki bar out by the pool is nice. Its technically on 7 mile beach although it is obscured from the beach by another property, but does have direct access to the beach. It is on a good part of 7 mile with lots of stuff within walking distance. Also, the bus stops are all over the place. Don Fosters has their satellite shop onsite, so you can certainly be picked up, as I caught the bus there.
The Courtyard (formerly the Holiday Inn) is a little further out on the north end of 7 mile, but I think they pick up there and you may get it a little cheaper than Comfort Suites. If Don Fosters will not pick up there, you can catch the bus for cheap. The Sunset House is usually available under $200, but it is south of Don Fosters and not on 7 mile.
I did some dives with Don Fosters and had a good time. I would also try to pick up some shore dives down at Eden Rock. You can catch the bus downtown for cheap.
