1997 Renault Clio Oil leak

Engine Mechanical problem
1997 Renault Clio Front Wheel Drive Automatic

I have an old Clio that has leaked drops of oil for a while now but the poblem has worsened. I put around 1.5litres of oil in and after around a month of driving the oil light comes on again and I need to re-fill it. I have had a member of the family look at the leak and he believes that it is a seal that has gone near the crankshaft. (The pool of oil left under the car is near the front of the engine on the drivers side) Unfortunately he doesn't have the tools to repair it so I was wondering a) does this sound like the probable cause and b) How much would it cost me to get fixed?

Cheers