I dealt with Refrigerant finders. I had a 30lb cyliner of DuPont Freon (R-12). Virgin cyliner, with original shrink wrap seal (that is barely still attached). Weighing in at 35.8lbs.
They offered me $17/lb initially, then offered $6/lb. I am assuming that they are looking for people who have no idea what the value of R-12 for a classic car is.