What is the best practice for grounding a shielded cat 7 ethernet cable?
Fibre/fiber is by far the preferred/best solution to the problem when running external to buildings.

It can be inexpensive or expensive, and that does not always correlate to quality. Typically the most afforable "fiber converter" is just a switch with SFP (Small Form Pluggable) [ or XFP slots if you have application for 10Gigabit. ]

The market has moved a great deal - at this point there are very affordable single-mode SFPs out there, and that makes the mutli-mode versions that have less range and need more expensive fiber far less of an attractive option. Likewise, the price premium for "reduced bend radius" singlemode fiber has come way down, as it's become the default single-mode fiber in many applications.