You seem to be very serious at getting this job. You spent countless hours both on preparing and on working to get interviews, on which you unfortunately failed but really wanted to get the job.
Your problem is not lack of preparation. It's actually the fact that you spend countless hours on “naive” practice, i.e., just putting more hours in the hope of getting better. That only works up to a point but never enough to get you to expert level.
To become an expert you need some purposeful practice or (ideally) deliberate practice. Both of them require you to know what to improve, and to spend time on a purposeful way, but the second means you will be guided by someone who can 1) tailor your practice to your specific needs and 2) knows how one can improve. I.e., it requires a coach. Just like you would have a coach if you wanted to become good at tenis, or at playing a guitar, or at many other skills.
I find it puzzling that you think that paying $150-250 for a single session with a good coach (make sure it's one that will give you coaching and not just a mock interview) is expensive. If you think about the hours you spend, the fact that you weren't still at your best for the job interviews… was your alternative cheaper or more valuable?
You have alternatives, of course. You can try to find someone who could be as good as a coach - someone with experience interviewing people that is able to tell you what exactly are you doing wrong, and how to improve it - and get him/her to do it for free. The downside is that unless you already have someone like that in your rolodex, you will have to spend several hours in that pursuit, and may not be successful at it.
The other option is to proceed alone, and resort to the ton of resources out there to help you improve (if you haven't yet). For example, you can go through the Bootcamp area at preplounge (https://www.preplounge.com/en/bootcamp.php) or watch the video tutorials (https://www.preplounge.com/en/consulting-frameworks). You may find useful stuff there. Just not sure how much different that is from what you are doing now, and how that can lead to a different result.
Sorry for the long “pitch” about coaching. I understand that coaching has a cost and it is not exactly cheap. And not everyone needs coaching to get the offer. But you already tried that route, wasting your own time and potential job offers. In your case, it really looks like it's time to take a different approach.
