You still have to take your bird to the vet, no matter what. As the owner, it is your responsibility to make sure the animal is healthy.
The previous owner just left the bird in this condition without taking it to a vet? Seems fishy to me. Did you buy the bird or adopt it from them? If you bought it, I would NEVER buy from them again. That bird is sick and need a vet.
If you cannot afford to take the bird to the vet right now, take it in anyway and pay for it over time. Seriously. Look for a job if you don't have one, or look for another if you already have one. Or you could borrow money from a family member, do odd jobs for people, sell some things, stop paying your cable bill for a while etc. And if you really just cannot take the bird to the vet... then you need to re-home it with someone who CAN pay for it or give it to a rescue. Period.