I have to say Jays Custom has some good ideas on cheap tools to build. This time he makes a pretty good sized moxon vise. Total cost I think would be $30. Which is allot cheaper than some of the pre-made solutions I have been looking at (well over $100).
http://jayscustomcreations.com/2014/04/how-to-make-a-sliding-moxon-vise/