Best way to replace2001 Mitsubishi Diamante transponder key?

son lost his only master key to his Diamante, trying to replace key without towing car to dealer and paying over $100 for new key

there's no way to get the key programmed without taking it to the dealer, on occasion you may be able to talked to the service mgr. and he may help make cheaper arrangments but they'll need the car at the service area.

been there done that...

The only way to do this is at the dealership. Not only do they need the car, they also need any remotes and valet keys you have. All these things must be programed now. Ask the parts department at your local dealer that if you purchase the key over the retail parts counter if they'll program it free of charge. The key itself should only be about $45.00. The service manager can also be useful.

Find a new car with a working key.