There is knocking coming from engine in my 306 even when ignition off so l think it is the fan??Does anyone know how much this will cost about to be fixed and if it will be ok to drive it to a garage?Please help!I've spent so much money on cars recently!!!

24 hours & No ?
Ok. So it may be the fan. (There r sometimes two fans! Here is a photo of ur 306 fans & complete technical info):
http://pethotel.hut.ru/peugeot306/CoolingFan.htm

Fans come ON at 97 degrees, OFF at 90 degrees, or when the Airconditioning is ON at any temperature.
The fan will continue to run when the engine is hot, & u turn off the engine. This is normal, but the knocking is not normal. Have u already checked for a plastic obstruction to the plastic fan blades? Let the car run when u first hear the knocking. (turn AC on if u have it?) Go to the front of the car & listen next to the front grill.
Or visually check from underneath the car with a torch (flashlight). When the engine is cold, u can spin the blades with ur fingers or a long, thin screwdriver, stick, pencil, etc.
You can also (if u r mechanically inclined) add 12 volts directly to the fan motor, making it spin full speed for a few seconds. Listen for fan blades knocking against something.

Yes, u can drive to the garage for this possibility. Be sure ur car is very warm when u arrive; do not just drive 2 miles to the garage & turn it off. Phone ahead to see if someone can listen to ur car upon arrival.

A new fan motor, l am guessing 25 pounds, & one hour to install. The inner protection must be removed & replaced.
On early model 306 is the radiator must be loosened & tilted backwards to remove the fan.