If the air conditioning system has not worked in three years the receiver drier for sure needs to be replaced but first the system will have to refilled with some refrigerant and then run to see where the system is leaking the leak could be in the evaporator, condenser, hoses ect.... the system could have failed due to the compressor in short its impossible to guess at a cost to repair until the system is filled with refrigerant and is got operating to see where it leaks. The leak is then repaired, the system evacuated and tested for other leaks then flushed out and refilled.