For different definitions of cheap though.

While the pure gyro/accelerometer stuff does suffer from major problems the improvements in SLAM using just cameras in the last 15 years are insane.

Visual SLAM on a rocket would be wild. The frame rates you'd need at those velocities are brutal though — feature tracking falls apart fast when your entire visual field is changing at hundreds of m/s. Drones are the sweet spot where camera-based nav really shines.