Adding terrain/obstacle awareness can be an incredibly difficult task, in addition to the fact that it requires the addition of a sensor suite to the aircraft (more weight). Smart flight planning and pilotage should be all you need.
Repairs are a mixed bag. It depends on what you break and how. I would expect that chassis parts are relatively inexpensive. Props, motors, and all the guts are pricey.
Crashing is a natural part of RC flying. I've crashed my fair share of drones and other RC aircraft.