Repair or replace usually depends on the age and price of the laptop.
If it is a new, high end laptop, getting the unit repaired would be the way to go.
If the laptop is over a few years old, trying to get replacement parts may be more that the cost of a new unit.
One option i have used is to look at computer swap meets / online auctions sites / etc for the same make and model with different damage and get it cheap to swap parts over.
Swapping the hinges and cover are simple if you take your time and record where you remove screws from.