Since the snake is not in good shape, they took on a possible bill-producer too. They probaly have the same attitude I have a lot of times. If someone only wants it because it's free, then they usually assign no value to it,a nd might not ake proper care of it. I'm NOT talking about the OP, there is always an exeption to every rule right? I'm sure you would be a great home, but they are a business to make money.
They took it in, they can sell it. $100 is about the going rate for most pet ball pythons at a typical pet store around here, so it doesn't surprised me at the price.
Think of this also, if they take in a neglected snake, it could easily need a vet visit for say ... RI. How much is that? Could run well over $100. So each animal they take in to rehab and resale can add funds to the amount they might need to spend on a later animal that needs more attention. I did the same when I took in unwanted dogs. Dog #4 might be in perfect shape, and get a home immediately. But dog#5 might have a broken leg and need $800 worth of vet care. So the other dogs I take in that are fine, and need nothing more than shots get adopted out at a fixed adoption fee. $100. Why? Yeah, I COULD give them away for free, but then who in their right mind will pay that $800 to reimburse me for vet bills on that ONE dog? I might be willing to take them in, rehab and rehome, but I can't foot that bill myself every time. So the $100 adoption fee for each dog goes to fund more rescues/adoptions.
Looking at it that way, I can't see that someone would say they are merely making money off a 'free' snake. Some places can afford to do it, and might. Ball pythons are pretty common, and I'd suggest you keep an eye open on places like Craigslist, classifieds, and all local vets, herp shops, and pet stores for people looking to give away their own neglected or unwanted animals. You're sure to find a great snake that needs you.
Wolfy