It is illegal under federal and various state laws for ANYONE to remove or tamper with an emission control device. There are not a whole lot of resources for enforcement, so enforcement activities are generally focused on commercial establishments.

Fastlane offers direct fit catalyst replacements that are less expensive than the dealer, but they are not what I would call "cheap".

I believe it's also illegal to sell used catalysts, so salvage yards won't sell them, even if they come from low mileage cars.

Given the cost of catalyst replacement you are well advised to seek out a definitive diagnosis on your catalyst. One way would be to remove an O2 sensor and fabricate an adaptor to accept a probe to check exhaust back pressure. At WOT high revs it should no exceed about 5 psi.

Duke