What counts as grounding conductor
Bare stranded copper, green-insulated copper, and the grounding conductor inside tray, MC and service cable. Sizes follow the equipment grounding table, commonly 6 AWG through 4/0.
Bare versus insulated
Bare copper is priced close to clean copper with a small fabrication premium where lengths are usable. Green-insulated conductor carries an insulation premium and is bought for reuse in grounding and bonding work.
Lengths that matter
Grounding conductor is often short offcuts. Bundled and measured, they sell; loose in a bucket, they are weighed.
Do not mix with scrap copper
Cut grounding conductor kept separate and measured will usually beat the same weight sold as scrap copper, because a contractor can use a 60-foot length.