if so then you will have to ask the airline as a good chunk of that cost will be the transport and the airport fees.
I assume you wont be bringing you dog back soon as the poor thing will be returning from outside the eu and will nee to be quarantined and also test ed upon its return as there is rabies and other infections for dogs in Tunisia.
Another issue if the breed of the dog many airlines will not take flat nosed dogs as they may die in storage on the place.
I don't think those quarantine times apply anymore Kris if I remember rightly. I think Gem knows more about this. They do have to have all their vaccinations in Tunisia before they can return and have them cleared before they can travel, but the long quarantine times back in the UK doesn't happen anymore.
Dogs can be taken back from Tunisia to the UK without having to be quarantined as we have check this out, as long as they have had up to date rabies injections and the blood has been sent to a recognised company to be tested in France. Also if they have been vaccinated and tested in the UK the dogs have 2 years to return back to the UK without quarantine.
I brought 2 cats from the UK nearly 8 yrs ago and it costs £1000 with Thompsons.