Sancho Vet Bills, snake bite. Please help my baby

My dog sancho was bitten by a snake yesterday. We took him to the vet and spent all the money we had for the what they would do for that much. He got one vial of antivenin and some fluids. He is not doing well and needs more help. Please help if you can. The vet is suggestion more antivenin and monitoring that will be an addition 3000 on top of the 1500 we already paid for his first visit.