Quote Originally Posted by grey View Post
How much does this switch tend to cost?

And for an idiot newbie like me, you're talking about taking out the 9-10 gears in the back and switching them out for MTB gears? Do you need to get a new derailleur too? Will it play nice with a compact double up front?
Ok, I'm not technically minded, but basically you're giving yourself the benefit of (or really close to) of a triple crank by only switching out the cassette (you can save your compact double crank). I tried this first because I'm a mtber for the most part and already had the parts and it's way cheaper than buying a new crankset (to add the granny gear). Most road derailers weren't made to accomodate a 32 or 34 tooth cassette, but mtb derailers are, so hence the new derrailer.

In terms of price, you'd be looking for a mtb cassette and a derailer (LX or XT would be fine).