What should I do with $3,800 mattress that I used for my Father and now is gone?

Only donate if NO bedbugs (ever) & NO body fluids of any type ever touched the bed (if they did, discard it).
If it is an air-pulsing type maybe contact the VA, church, synagogue or elder-assistance or hospice/homeless center?
They may not be able to handle the bed directly, but might be able to refer people to you.

If it is a "regular" mattress or foam you may just have to take it to the dump (also, if your Dad died in bed some people have the heebie-jeebies about that).

Objects in this world are created, objects are discarded. Just the way of things.

We have an assistive tech place in Arkansas that takes those kind of donations pretty commonly...is there anything like that where you are? And selling it online with photos showing it is clean and in good shape, probably "local delivery only" option would not be unheard of or wrong, I don't think.

Health Department regulations.

Is this one of those alternating air bed mattresses? It's a shocker that no one seems to want it, I agree. What about calling your local hospice organisations and seeing if they have any immobile patients who need it?

Use it or have a bon- fire w/ smores & roasted weenies on sticks! Invite me & I'll join you! We can all yell, "Burn, baby burn!" We can play music & tell ghost stories & lay around the fire in our sleeping bags....... Well, we'd have to drag it to a safe, legal place to do that & it'd have to be safe w/ water near by.....I was a girl scout, I got this!@ No worries! OR you could put aplastic cover over it & lie outside this summer & stare up at the stars with your friends, grand-kids, whomever... I IS a great mattress, right? DO something FUN! ((& invite me over! hee hee). blou

Sorry. Call your nearest Goodwill/Salvation Army/Amvets. They will have to fumigate it and recover it before it can be sold. Don't even attempt to cross a border with it e.g. US/Mexico/Canada. No go.

It seems like a BIG waste but no one wants a used mattress anymore. Bed bugs is probably the main reason.