You may not find your desired cars at most rent-a-car companies in Doha. Suggest, you write to major ones in Doha such as AlMuftah, Budget, AVIS, Europcar, Hertz etc. You can get their contacts through Google.
Car rents vary from company to company, to the type of car and also for the period of use. As such, it is not possible for anyone to give you an indication of the costs involved.