Q: Tainted gas repair and routine spark plugs replace, $2500, is this fair?

That seems a little extreme. It helps to know what kind of contamination you are talking about. For instance, if the car was vandalized and someone has put sugar in the gas tank, then you will probably have to do some pretty extensive repair and I could see the cost going that high. But if you have filled your car with diesel fuel, which is a very common mistake, then the repairs may not be so extensive. The fuel pump will probably need replacing, as it lives in the fuel tank and that may be expensive. but it may be possible to pump the tank empty and fill it with gas and let the gas flush out the rest of the system. If the car has not been sitting full of diesel for a long time, the damage to the other rubber parts may not be significant. To get another opinion and estimate on this job, you can contact Your Mechanic. They can send a technician to your home or office to check out your Lexus and tell you what it is going to take to fix it.