I wonder if 10 speed stuff is a step too far, It seems that everything costs double compared with 9 speed. I do like a lot of gears as I use leg power as much as possible but it seems a lot to pay for the privilege of an extra cog. I've tried a friends 10 speed bike and I could certainly feel the difference but not enough to make me want to upgrade. It was a new bike and strangely enough he hadn't noticed it was a 10 speed!.
My last Sram 9 speed cassette and matching Sram chain cost just less than £30 for both though as Martin said, spread over the mileage, cost per mile and cost per smiles isn't that much.
Dave.