Whether this snake is a pet or considered stock in a business, you incurred responsibility for it's care when you bought it, for whatever price.
You tried the home remedies. You've done what you can to save money and help your snake. It hasn't worked in this case. You now have two options. Continue with plan A and watch your snake deteriorate or plan B, cut your losses and bring the snake to the vet so that proper treatment can begin. If money is the only concern (like a pet store for instance) then it will be cheaper and more humane to have the snake euthanatized.
I've said this a million times on these forums, take your animal to the vet. I wouldn't be doing you a favor if I said anything otherwise.
As far as reasoning goes, from the picture and your description here is my opinion on what has happened and what needs to be done. Keep in mind that I havn't seen the animal and only a vet can diagnose pathology.
My first thoughts is that the many, many parasitic bites took a toll on your snakes skin; a very important part of your snakes immune system. Because this barrier is broken and weak it is now permeable to bacteria fungus and infection sets in. Already taxed with the stress of importation the snake puts on a weak battle and the infection soon enters the blood stream spreading all around the body. What you can see has spread, dramatically according to the pictures. What you can't see is the growth of bacteria withen your snake and the subsequent colonization in the bladder, kidneys, heart, lungs, liver ect.
You are on the right track with assuming that antibiotics are needed however you made a misinformed decision to try and circumvent the proper method of obtaining them (veterinary prescription). After examination your vet may give you an antibiotic (cost considering) at the proper dosage, and of best guess as to which one will work. What your vet would really like to do is preform bloodwork and see just what this infection is doing to your snake. This will give your vet a much better picture on what method of treatment is safest. For example, if your snake is dehydrated and he/she gives you amakacin, your little critter's kidneys are as good as dead. You see, it is not just a matter of giving the drug, it is a matter of predicting what it will do once in the body, where it will go, how it will be metabolized, and how it will eventually be excreted. Another test that can be invaluable is a culture and sensitivity. This is basically taking a sample of the bacteria assumed to be the cause of the infection and testing to see what antibiotics will kill it.
I realize this is a longer post, but I truely hope that I've really helped and any critisism has been constructive.
