Our opinions of what the trailer is worth won't help you I'm afraid.

Contact Merhow to see if they can help you in the repairs...I can't think of one company that doesn't need a tax deduction!  (Only you will know if you set the rescue up as tax deductible.)

Perhaps you should send your agent/adjuster a copy of the Bill of Sale showing what you paid and when.  The fair market value is what a willing seller and a willing buyer agree on, on any given day for an item. 

As far as starting a non-profit animal rescue, please be prepared to pay "out of your own pocket" endlessly.  Perhaps a reconsideration of the rescue idea is in order.

Personally I would donate money to an already established non profit rescue org in your area. I googled and there are several already established.  It is expensive to start one and the attorney cost is around $500-1500 to get it set up with the governement for you.  (Trust me I already looked into it two years ago).  If you think you will come ahead with donations etc, think again.  Most rescues are knee deep in the red. 

I give you credit for wanting to do something good.  But you have to also consider that this trailer was a drop in the bucket of what it costs to run and maintain a rescue.  If you are having trouble with your insurance company on this, imagine the trouble they will give you when it comes to the liability portion of having all the rescue horses on your property.  That is right, you are supposed to have liability insurance should any of those horses escape or hurt someone on or off your property.  You provide care and custody, you are liable for them.  If you plan on placing animals, you have to understand you are liable when a person sets foot on your property to see the horses.  If they should get bit, stepped on, kicked, etc, or even get ringworm from a horse, you are liable.  The attorney went over all of this with me. 

Just a word of advice, think long and hard if this is what you want to do.  I would suggest you have at least ten thousand in cash set aside to aide in your start up.  I had about 8,000 and went through it all within a couple months, for feed, vet bills, farrier bills, paying folks to help out with mending fences, fixing stalls, cleaning, etc.   My husband makes good money, but not enough to go through 8k every couple months!!

Good luck and hope whatever you decide works out for you.

Do you have photos of the trailer from before it was wrecked? Would the last owner have any?

I'm sorry that you had an accident and I am glad that no humans were injured.  I agree that a stock trailer with full rear doors is a much better type to have for rescue work.

I agree with Mrs Tactical...  you might be more effective if you were to work WITH an existing rescue. Many rescues need people to foster horses - in other words, care for them during investigations, or until new homes can be found. Existing rescues will have already established themselves as a non-profit and have their marketing / fund raising in place.

So long as the rescue is a 501(c)3, you should be able to keep track of all expenses and/or revenue (if you are paid to care for the animals by an animal control agency) and then apply the amount on your taxes. (Your specific situation may vary).