The fact that you're asking the question proves that you don't even know what the term means. "Price fixing" is when (nominal) competitors agree to "fix" the price amongst themselves. Since you found such a substantial difference between competitors, that's proof that they are not price fixing.
Please leave economics to people who actually know what the hell they're talking about.
"Who gave them the right?" Do you envision a board of government agents somewhere determining what the permissible price is? You say you understand capitalism, but your question again betrays the fact that no, you really don't. Sellers free to charge as they will, and buyers are free to buy or not, as they like.
Buyers are NOT free to buy or not if they like, sure if you would like to remain ill or get even iller and DIE! Sure thats a great justification, Ok maybe price fixing isnt the word, How about profiteering? Horse crap that its been brainwashed that "capitalism" makes it just peachy keen and ok to charge ridiculous amounts of $ for pills made in INDIA for $.00000003