Imo you need to find a regular dentist, and not just limit yourself to holistic dentists. Holistic dentists probably won't accept any insurance, or be willing to do the work at a greatly reduced fee rate. You probably should just tell the dentist that you are worried about your teeth and that some of your fillings might be in bad shape, not your greater plan to have all your mercury fillings replaced whether they are in bad shape or not.
Try to find a dental school, or social services agency that can provide free dentists, or dentists who will work at a greatly reduced fee schedule. Don't look at it as an all or nothing project. Get what you can get done(ie the fillings that are in worst shape), and leave those that are in better shape for a later time.

I made the mistake of not seeing a dentist for over 4 years until one of my teeth became so bad that I needed a root canal. The priority for you should be to get the fillings that are in bad condition taken care of ASAP. Those are probably leaking mercury at a much higher rate than the fillings that are in better condition. You should plan on taking care of the fillings over a few years, so you need to start the process ASAP.
I had 25 fillings. It is almost a year since the last of my amalgam fillings were replaced. At first I felt much better after a few were replaced, however I have had several ups and downs since then.