I have found vocal coaches, online, who charge $450 an hour, $400 and hour, $200 an hour, and as low as $135 an hour. I have also noticed that they are using the same or nearly the same warm up and vocal exercises. Most, if not all of them, have studied with one particular vocal coach OR coaches who have studied with that very same vocal coach.
Most of these vocal coaches also claim having taught various famous singers. It is interesting to note that the vast majority of the famous singers were famous prior to studying with the vocal coaches. That's not a bad thing because singers have issues. I had my own, which is why I studied so extensively. I paid $175 an hour in Las Vegas. I don't regret the time or the money spent. Could I sing before I studied? I was in a show and being paid for it. Athletes have coaches, singers have coaches, business people have coaches, Some people have personal trainers, and some people have life coaches. Remember that the vocal coaches did not necessarily "make" those singers famous.
The question is, will you get more from a $450 coach that you will from a $45 coach? It depends on the coach. Some people teach voice, not having a clue that everything they teach is completely false and scientifically inaccurate, as has been verified by many physicians. To think that a $450 dollar coach is better, wiser, smarter, or knows all the "secrets", may be quite naive. Most people cannot afford very many lessons at $400+ per hour. To think that in one hour with a $450 per hour coach, that you will learn SO much that you never need another lesson, may be delusional. You don't take one flying lesson and then think you're a pilot, unless you are delusional.
There is a saying that "you get what you pay for". It is not always true.