The problem is that no other federal agency issues licenses to operate, like the FAA does. When one takes a checkride from a Inspector, one doesn't pay for the checkride; it's a function of the FAA. The FAA is required to give checkrides.
The FAA attempts to expand it's base of manpower by the designated pilot examiner program, and rather than funding the DPE's, the FAA allows them to charge applicants. If the FAA standardized the fees or set limits, that would be one thing, but the FAA doesn't.
The FAA limits the number of DPE's. It's not a matter of competition. Many are qualified to be an examiner, but the FAA doesn't simply allow anyone who is qualified, to be an examiner. Very few are allowed to be examiners, and these few hold a corner on the market, and charge accordingly.
In some cases, the extreme conflict of interest of paying an examiner to give the test bears fruition; the examiner becomes known for granting certificates based on the students payment. Some DE's in the USA do this very thing, and thus run pilot certificate mills. One particular Las Vegas operator is known for the very thing
A student shouldn't have to pay to take a practical test. So long as the government requires the test and issues the certificate, the government should provide the manpower to test the applicant, and the applicant shouldn't have to pay. The applicant already pays taxes, and the FAA is a taxpayer funded agency. To require that the applicant take a practical test for a certificate, rating, or privilege, and then to authorize only a few selected individuals to administer that test, and to allow them to charge anything they like for something already paid by the applicant as a function of his or her government taxes is not only an outrage, but an ethical compromise. It defies the FAA mission: "to provide the safest, most efficient aerospace system in the world."