if your looking for something cheap ive seen people use window cleaner, but as most have said a decent lense should be anti fogging anyhow and what fogs up a anti fog lense no cleaner or calotherm will stop
Been using this for a while, works awesome. (You may be able to find it cheaper, I just quickly googled the name). Only prob I have had is that it gets a bit dusty if you leave your lens lying around, but you can just wash and re-apply, the bottle lasts ages.