it can range from as low as $4 - $20+ depending on what type of capo. the cloth type will be really cheap, but it's not as effective. and i dont think anyone uses it anymore
the metal clip on type will be more expensive. about $15 for an average one maybe. it's a lot more convenient and useful.
they can be found at most music stalls. just head down to the nearest one to your place. i'm sure it can be found there