Thiosulphate plus sulphite is a good long lasting fixer. Have a look at:

http://www.heylloyd.com/technicl/plain.htm

The only issue might be that "new technology" films are supposed to fix better (or at least faster) in an ammonium thiosulphate fixer (i.e. "rapid fixer"). I don't know if rapid fixer is necessary.

One advantage of using a cheap fixer is that you can be a bit more generous in discarding used fixer before it causes damage (more of a problem with paper than film).