Ian,
Sorry for being negative, but I have seen others (and been myself) ripped off by people offering flights at a cheap rate for what amounts to nothing that can go in the log book. I know exactly what you are trying to acheive, having had those exact same thoughts myself. I am not sure how much experience you would gain from the trip - it all depends on the attitude and professionalism of the pilot. I would have thought that at your stage, you are better sharing flights with more experienced PPLs and then once you have the CPL, go for the trips with the aerial photographer.
I am not being sceptical about this - the rules are very plain. You are crossing the line into professional aviation here. None of what you might do on such a flight is logable.