You do know that, unless you have an instructors rating, only the person flying as P1 can log the time in their logbook, don't you?
In that way, although you'd only pay for half the flying, you'd also only be able to log half the hours. Of course, there are benefits, like being able to fly further, and have some company etc, but you still only get the hours you pay for.
Just thought I'd make sure you realise this.