All the sentences are correct. In the context your examples indicate — “bargain on” and “bargain for” can usually be used interchangeably, but “bargain for” is more common and sounds most natural to me. They both mean “to expect,” but they usually used in the negative: “I didn’t bargain for/on X” — meaning, I didn’t expect X. “Bargain on” can also used in this context, meaning to buy something at a good price: “I got a bargain on that car. I paid $5000 less than the usual price.”

http://learnersdictionary.com/definition/bargain%20for bargain for/on [phrasal verb] bargain for/on (something) : to expect or plan on (something) The Internet service is better than what we bargained for. [=better than we expected it to be] No one bargained for the change in weather. = No one bargained on the weather changing. They bargained on getting married after college. He hadn't bargained on how his new position in the company would change the way people treated him. [=he was surprised by how his new position changed the way people treated him] The job ended up being more than I had bargained for. [=more difficult than I had expected] I got more than I bargained for when I signed up as a volunteer. [=being a volunteer was harder than I expected]