Does anyone have info on the least-expensive way to replace a missing master key for a 2000 Lexus ES300? The only key I have is a valet key.

 

Cheapest way is to find the key.

Failing that, the only way to get a new master key working correctly is to either have the ECU reprogrammed (by a locksmith, Lexus will not do this), and then register the new master key with it, or replace the entire ECU with a new one from Lexus, and do the same.