are you doing it your self?
Is the water damage just on the lower couple board?
Is it wood?
If the answers are all YES; take off a piece of the siding and take it in to H.D. or Lowes and have them match it up. Most Siding is pretty cheap. Us the right screws or nails and you can probably get by cheaply.
If the answers are NO, we never met and you don't know me.