When I started reading your post, I was inclined to say negotiate a reasonable price and "rescue" that snake. After reading the responses, I have to say I completely agree with their reasoning. Buying it to save it just gives the pet store money to repeat the cycle. If you can avoid the store completely, I say do it and protest by closing your wallet to them but I see that may not be an immediate option for you. Depending on how well you know the manager or employee, I would recommend 200xth suggestion: speak to them about a better housing. They may or may not heed your advice but at least they'll know someone is noticing their treatment of the animals.

I have a similar situation with a local pet store. They have very little knowledge of reptile treatment and I've made it clear to them of all the things they are doing wrong. Nothing has changed so I now go elsewhere.

Hope you'll update us on what eventually you decide to do. Have a good one.