Any dog that is bleeding needs to have lab work done. You could ask the emergency clinic to at least do a CBC and ask their opinion about how he might do through the night. If he has HGE, he could die at home tonight. Bleeding is serious.
Here is a link about HGE:
Hemorrhagic Gastroenteritis in Dogs | VCA Animal Hospitals
Perhaps you can apply for Care Credit...IF he has HGE, the treatment is not cheap. You really need to think of a way to get some money together if he needs hospitalization. BUT for now...find out what it is!!
No, I would not suggest you get insurance first. It won't cover anything that happens that same day. And forget Banfield...they have a wellness plan where they push a lot of vaccines that are not needed. For sick care they are horribly expensive.
My opinion: Go back to the EC and have them do a CBC .. at the very least! You could ask them to whittle the bill down and do the most important things!