I'm not sure why you are looking at alternatives to stainless steel. You'll end up with it in the end.
316 grade is used in marine, medical implants, industrial chemical handling etc.. (there are different grades of 316 BTW). 316 costs 5-10% more than more basic grades, but it's all pretty cheap.
As for how to seal it in the casing, I would use o-rings to seal it - lots of different grades again (VITON, rubber, butyl, nitrile, etc...) cheap and reliable.
To make the electrical connection, you could thread the ends and use a ring terminal, crimps are another good way, even use a piece of choc-strip. Even battery springs will work well and are cheap (god love Keystone Electronics).