I have LIDAR in my Audi A8. It is an option for 2900€ ($3,245). I doubt it would add $20,000 in price to a Tesla.
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It's also very different from the LIDAR used by FSD candidates from other companies.
It's not obvious how capable a LIDAR is necessary (especially since it isn't obvious that a LIDAR is necessary,) but there's a wide range of capabilities and related price points in LIDAR, and folks claiming Tesla needs LIDAR mostly seem to be pushing for the top end pricy stuff used by Waymo and Uber.