These are usually pretty expensive, but the Micsig probe in the video costs under $200. The question, of course, is what do you need with a differential probe? A typical scope probe has a ground ...

Improvements over previous Micsig models include an intelligent bidirectional Universal Probe Interface for accommodating and powering smart probes such as those with differential inputs and new ...

A differential probe, a device for measuring the voltage between two points in a circuit rather than the voltage between a point and ground, it an extremely useful addition to any electronics bench.