Some forks, such as those equipped with Fox FIT dampers require more time, and will cost more. Forks other than Rock Shox or Fox will be sent in for factory service and may require more time and a different price.
With some shocks, this will be a factory service and will take time to send back to the manufacturer or service center. Some shocks also require more work than the $150 allows, such as the Fox DPX2. These types of "piggy-back" shocks will be subject to price increase due to the additional complexity.