I went to Greece in 2005, Turkey 2006 and am going back to Turkey in 2008.
To be honest we didnt see much difference in price between the holidays in 05 & 06.
We had similar style holidays. family of 4, two weeks AI in school summer hols.
The holidays cost the same price and we used about 1K spending. We ate out a few times to ring the changes, did 3 expensive full-day Thomson trips in Turkey, but hired a car for the fortnight in Crete (hubbie wont drive in Turkey
), these two costs were about the same, so kind of cancel each other out.
The Euro rate has suffered but so has the Lira, so I would just choose the one you fancy.
Re Greece, I think that the costs can vary from Island to Island, ie somewhere 'posh" like Santorini or Skiathos, is much dearer than a main stream Island like Crete, Rhodes, Corfu etc. I don't think this happens in Turkey so much.