any dog can be a therapy dog if u are on a waiting list maybe hold a fundraiser thru the school for him also have you checked into paws with a cause

You can also look into a training program for a puppy you want to get from a shelter, breeder (a reputable one please), or if you already have one at home. Even if they are older, they can still be trained, but just need to make sure they have the right personality.
There are trainers who do Canine Good Citizen training. It would still end up cheaper than getting a service dog. If you don't already have one, just make sure you get a breed that can tolerate possibly being rough handled by a kid and can support him/her throwing their weight around on the dog. Even mixed breeds are good, no need for it to always be a golden.
I have two 8 month old lab/pit bull/cattle dog mixes that are amazing with my son. One of them actually always keeps his paw on my sons lap to apply "pressure". Sounds weird, but dogs can sense things and know how to help at times. And to some it comes naturally.
We do have a trainer we have worked with before with other dogs I've fostered and he thankfully provides the good citizen training. We'll be registering both puppies soon.
OF COURSE the only down side to this training is that this wont make the dogs therapy/emotional support dogs out in public. You can register them with the us dog registry and pay for a certificate that will give them a vest and certification.

I'm just giving you my personal opinion. Everyone looks at and does things differently.
A fundraiser is always a great idea, besides looking for grants/scholarships online. Try the go fund me page and anyone can donate to your cause!
I do wish you luck!