For the actual monopod I don't think you can go wrong really. Unlike tripod monopods are much simpler and there is less to go wrong. I picked up a $10 job form walmart, solid steel and good clipping mechanism, very sturdy, no flex. Not very light of course but lighter than a good tripod.
Getting a good heady for the monopod is another matter. I have a Really Right stuff BH-30 in mind for mine but might go for a cheaper option but you tend to get what you pay for here, my RRS BH-50 is outstandingly good and worth every penny.