Will it be cheaper if I want less data?The price generally does not depend on the amount of data required. The cost of recovery is dependent on job complexity.
Most of the time, data stored in the media is scattered across all data zone. This is more so after constant file write and delete, program install and uninstall. In order to perform a recovery, the whole disk may have to be scanned so even if you have 1 GB of data in 100 GB hard disk, we still need to look into the 100 GB disk space.
As another example, you have a disk with read write head crash. To recover all the data or just 1 MB of data will require the same complex procedures of servicing the damaged disk in our clean lab.
Most of the time, it is the value of the data, not the amount of data that is important in data recovery jobs.