If you attend second look weekend, you'll receive a book or packet of information with years of collected reviews from upperclassmen and former students on housing around the area. They may also take you around to a few places, just to give you a feel. If I remember correctly, once admitted, there's an online exchange as well where people can find roommates and respond to available housing arrangements (usually from the graduating 4th years or other upperclassmen).
Essentially, no one lives on campus, though grad on-campus housing is available. It's not recommended. Housing off campus is very affordable and convenient. Generally, areas immediately around Duke and south of Duke are safer than areas north of Duke. My classmates live in shared houses for as little as 300-400/month or in upscale gated indoor communities (pools, basketball courts, entertainment rooms, 24 hr security, etc.) for about $1000+ for a 1BR. Plenty of great options in the middle, too. I wouldn't stress about this!
