Thank you for giving me a clearer picture of what’s going on. Oh golly, this is a lot to take in, isn’t it.
I’m going to combine several of your replies today. Sorry for the delay, I was on the road and not able to get back to you.

To answer your question. I am not an dentist but I do have dental education background, specialty training in several different areas of dentistry and 30+ years experience as a certified dental assistant. So while I am familiar with situations like yours, I am not in any way diagnosing or telling you what to do. I’m just using my experience to help YOU make some informed decisions.

Let’s tackle the All on 4 first. You’ve had several dentists look at this option for you and all but one said, “No”. That’s very telling and I’d go with the popular opinion.
Since your original post mentioned you had a collapsed arch, that would be the reason it isn’t advisable to have 4 posts (implants) holding a full upper arch of 14 replacement teeth. That could potentially end up shifting as there is no support for the arch…too much pressure without palate stability.
The other option presented to you was having implants on the upper to hold the denture. The upper implanted posts would not have teeth on them, but rather, they are posts at the gum line that allow a removable denture to be affixed to them. That stabilizes the maxillary (upper) arch and still gives you a full smile with the ability to eat without having the adhesive on the upper plate. Also easier to keep clean.

Lower dentures are done the same way if needed. However, since it sounds as though your lower teeth are ok? Maybe a partial denture would work on the bottom. You could have your two front teeth crowned to preserve them. Then have partial denture for the bottom to fill in with the missing 4 molars.

I’d make sure those 2 teeth on the bottom are really stable before I’d put crowns on those. If your other remaining lower teeth are not affected by bone loss, you could have the two front teeth extracted and have replacement teeth for those 2, along with the 4 molars added to the partial denture. The partial would affix with clasps to the remaining bicuspids. I posted a photo below. Only for a rough idea. It is not exactly what yours would look like.

Personally, I think you should be honest with your dentist and tell him you appreciate all he’s done and would really like to do this work. But that you simply can’t afford it. Ask if he has any less expensive options he could offer.
And, that you would like an exam at the dental college to see if they may take you on as a patient where it can be accomplished for a lower cost. You have every right to do what’s best for you!
You can request your records. It won’t anger the dentist!

From experience we made every effort for our patients to accommodate their needs. But I do remember a couple of patients we referred to the dental college because they were great candidates for the new dentists and were able to get their work done for less. You can assure your dentist that you want to continue with his office in the future for cleanings and exams. What’s the point of having these marvelous new teeth if you can’t afford to buy food to eat when they’re done?

That leads me to my next question. Are you on a 4 month recall program for teeth cleaning? Did the hygienist do a root planing procedure to help correct your periodontal disease to get your bone and tissue healthy? What is your routine with your dental office?