How much would it cost to replace laptop keyboard.?

I have a Compaq Presario CQ61 laptop, and I've broken the down arrow off of the keyboard. Normally I can replace the keys, just the clip that attaches the key has broken so I can't hook it down. The rubber 'spring' is still attached. Is it possible to just replace this key, or will I need to replace the whole keyboard? How much would this cost, approximately?