Old Key West is the first DVC resort. They set the points at the level they decided on at that time. When they built the other DVC resorts, they raised the point costs a little. However, they promised their first DVC members and couldn't raise the point costs later. Therefore, OKW costs much less point-wise than the other DVC resorts.
The $$ costs of the resorts is MUCH higher. The dollar cost of points to cover 6 days of a grand villa is about $1,500 at value season (286 points). That cost is the purchase cost for a single year of those points (along the life of the contract) plus the maintenance cost for those points. The cost to rent those points from a DVC member would probably be about $3,000. The direct cost of that same rental would be $6,600.