My son has an LS430 with two bad cats because his valve.cover gaskets were leaking and they had excessive blow by. He's a broke college student and 2K per cat isn't going to cut it. Has anyone used an OEM car with success? Yes I'm very aware OEM is better but they are way outside his budget range. Just wanted to see if anyone has had any success with other brands.

 

Take the cats off and clean them best solution

 

valve cover leaks - leak oil externally , and would not harm the cats. Blow-by is oil being burned by the engine , and that could harm the cats. Blow-by is usually worn piston rings, which requires an engine rebuild to fix.
you can try to clean the cats using the Pakistan method, all you need is a gallon of diesel and a salad bowl

 

He might have meant valve stem oil seal leaks. When worn out they let engine oil into the cylinder and can clog up CATs.
The diesel cleaning method above works to unclog the matrix in the CAT but if the Platinum/Palladium/Rhodium coating on the matrix has worn off then new CATs are the only fix.
Aftermarket CATs are mostly pointless unless you are fitting a high-flow exhaust system and tuning the motor.