Take a dropper and fill it with water and very SLOWLY release it in his mouth directly. His natural reflex will be to swallow. It might be time consuming but unfortunately it is probably your best course of action. This will also let you measure how much he is drinking.

As for the financial side, it is a bit tricky. Far too many people get dogs without the foresight to put aside at least $5000 or more for veterinary emergencies but the reality is that it happens very commonly. If your vet can give you some treatable prognosis (ie brain tumor) you might have a couple of options. You can try crowdfunding and asking for financial help from friends/family and you can also try asking/looking for a vet with a payment plan. But that all depends on how much quality of life your dog will have if his situation is treated (some cases it is just better to let them go) and amount of time, resources, etc. you can currently devote to his care.

I am sorry for the place you have been put in but hopefully you can find a solution that you can be at peace with.