A taxi is about 90 euros, you can get cars for 20 euros a day.
If you know someone who does it for 90 euros - be very careful - if they are not a proper taxi they may not have public liabilty insurance, and if anything happens you could have a real problem and be paying the same price.
Chris, Manchester - Gibraltar is due to start again in Sept/Oct I have heard and Gib to DV is about 32 euros by taxi.
Malaga Airport to Marbella bus is about 5 euros per person