X2 on the above post. The quality of the birds will have a huge effect on the price as well. Ducklings from show quality or breeder quality parents are going to cost more than the ones in your local feed store.
If you really are physically located in Pakistan, that is going to be a much better option for you if you're just looking for pets and/or egg-layers. Between the shipping costs from Metzer and all the paperwork you'd need for export/import (health certificates, etc.), you'd likely be paying as much per bird for a regular hatchery-quality bird as you would for a show-quality bird here, and possibly even more.
I've never seen ducklings sold in pairs around here, only mated pairs of adults, but it sounds like you'll get a good price there if you're just looking to get some ducks, and all ducks are good ducks