I generally am too cheap to buy organic... but I heard this once and I think its a great philosophy to use when you're making that cost vs. healthy decision.
If you eat the skin of the vegetable/fruit its a good idea to buy organic, if you're just going to peel it away, save your money.
I know some of that nasty shit can get inside too, but if you have to be cost effective- its a good place to start.