Trimble allows transfer of classic licenses between individuals. You can buy a used SketchUp Pro 2019 license from someone selling theirs (e.g., on eBay or specialized forums). Prices typically range from $150–$400. Not free, but cheaper than subscription.
: Users could pay an optional annual fee (roughly $120) to receive updates and technical support. Sunset of the Model sketchup pro 2019 classic license free