Dog has 99% liquid diarrhea with blood, won't eat, and is very weak with no energy.

To start with, i really want to take him to the vet but something screwed up at work when i got the job and now I can't enroll for the pet insurance benefit until November. I really cant afford a large vet bill so I'm trying to make it the last resort. If nothing works I'll take him anyway but I have no idea how much this might cost and can't afford much right now, so I'm looking to see if theres any experience with this.

He is about 1year and 6months old. I adopted him off a family last year and they said he had his shots already. But being my first time adopting, i had no idea there was paperwork to be had. I plan to see if i can track them down but i might not be able to get those papers. Maybe theyll need to have shots again but i dont know if it's related to this. He is generally very active and always jumping around full of energy and playing with his sister. He usually drinks a lot and pees A LOTTTTT. On Sunday while I was at work, someone else took him out and said there was a little blood in his stool. When i took him out on Monday, it was 100% liquid and very red. Im not sure of how much of it was blood and how much was diarrhea. It was as liquid as water.. not a smoothy. But after he still acted normal, played with his sister. He seemed interested in food so I put it away for later.

The next day (today), I took him out.. normally he barks and runs around because he cant wait to go out. But he just laid there and looked at me. His poop was less red than yesterday and smelled really bad. There was also a small mucousy glob in it that may or may not have been just bloody poop. I wanted to take a stool sample to the vet but his poop is too liquid right now. He either got poop or dirt on himself so i used the hose on him and i noticed flies and little bugs being attracted to him but not his sister. I dont know if it's just because of that or it matters so I'm adding it. His appetite seemed a little off for a while now, but it has happened before and fixed itself when i changed dog food. This time I'm not sure if it's the food because its the same one he was eating just fine before but he's definitely lost weight and it's concerning. He wont eat. He also didnt drink as much as he normally does. When he peed, he stayed in the peeing position for like 30seconds to a minute after he wasn't even peeing anymore. All he wanted to do was go back inside and lay down. His sister is acting normal and playful.

Any advice is much appreciated. In spite of financial problems, i will take him to the vet if there's nothing else i can do.