This happened to my dog last year. He is on the bones and raw food (BARF) diet so he eats mostly raw chicken and raw chicken bones plus fruit and veggies.
He started throwing up everytime he ate, then eventually just quit eating and anytime he drank water, he would puke. He got to the point where he didn't even want to leave his dog crate that he sleeps in at night.
If I remember right, the doctor gave him something to calm his stomach and he also gave him some fluids (IV? It didn't take long). It took him an additional 2 days or so before he started getting back to his normal self.
I would probably contact a vet to see if they could prescribe him something if you absolutely can't afford to bring him in.
Dogs can go without food for several days, but you should still try to get him to drink. Start in small amounts, and work your way up for both food and water. I gave him water with those plastic medicine droppers (or plastic syringe) for kids and slowly squirted it in the side of his mouth since he was almost too weak to drink from a bowl.
For food, once you can get him to hold water down a bit. Try giving him some things that you might eat when you're sick. Crackers, apple sauce, yogurt, etc.
Good luck! Keep us updated!