Hard, dark colored skin is a normal abnormality. It sounds like it is dead skin tissue because the abscess has gotten so large that it has damaged the blood supply to part of the skin. This is really bad in rabbits as they are generally not able to mount an effective immune response to systemic infection and dead tissue left on a wound is a common cause of systemic infection. The vet I work for almost never sees a high white blood cell count in rabbits because most of the time by the time the infection has gotten bad enough to cause a high white count it has gotten so bad that the rabbit has died. Is there a possibility it will "burst" on it's own. Not really. Like I've said at least three times before, rabbit abscesses are not like abscesses in most other mammals! It will eventually get so big that the skin over part of it will die and start to slough off, but the infection will not simply drain out because it is a thick chunky substance and it will stay where it is and continue to get larger. Then you have a rabbit with a huge open wound that has the potential to pick up a secondary infection in addition to the original abscess itself. And again, I can not stress enough the danger of killing your rabbit if you use the wrong antibiotic! Having an antibiotic that you can purchase over the counter on hand may not only not be enough to treat the infection, but the antibiotic itself could actually kill her if it is the wrong one.
Would most vets be able to treat a rabbit abscess? Debriding the abscess itself is not a complicated procedure, and any vet should have access to all of the information they need about rabbits and special requirements for medications, so any vet should be capable of doing it. However, some vets simply refuse to treat animals that don't fit into their "comfort zone." Sometimes it's because they just don't feel comfortable treating an animal they are not familiar with and they are very uncomfortable with the unfamiliar. Sometimes it's because they are concerned that if anything goes wrong an owner will sue them because they don't have experience treating that particular kind of animal. Either way, it's a vet-by-vet kind of thing and you would have to ask your vet if she would be willing to take it on and what kind of payment plan you could work out with her. As for medications, that depends on what kind of medications she thinks your rabbit will need. I don't know what you mean about a "straight fee" for medications, every vet I've ever worked with has charged based on the amount of medication you receive (unless it's a medication that they don't normally carry, then it is common practice to charge for the entire minimum amount they would have to order even if you only need to use a fraction of that amount). As far as I remember, most of the antibiotics we use in rabbits are not the most expensive ones we carry, but every vet charges differently so YMMV.
