Since we cannot see your grade, the layout for the ability for equipment to get in and access the work area, it is almost impossible to gauge if the price is right. Understand that if you want the piping in the same exact spot it lays now, I would venture to say that the old piping will be removed and pitched away. Make sure that when they do the work that grillage is used for instant compaction at the bottom and around the piping so that the backfill doesn't create bellies or low spots in the new piping system. 57's, 6/10's, lime dust, pea gravel, bank run, or lime dust should suffice. There are some escavators that can cut the bottom of the ditch level to the pitch of the pipe, but very rare and the grillage will prove worth every penny to maintain proper pitch of the piping, years down the road.