Originally Posted by oddball

Look for some Origin8 cranks online. They're cheap, under $50, they look more expensive though. If your bike is newer with some fancy bottom bracket you'll have to buy a traditional square taper BB, shouldn't cost much. You can get them in 155mm length, many people with knee problems find these to be the cure. If you're running a road triple, 130/74 BCD, you should be able to swap your chainrings over.