The second GamePad will be expensive, but the American version isn't even having the option to buy a second one until later down the road sometime. You will rely on the warranty to replace it if it breaks or something. The reason for this is because there are no American games that take advantage of two GamePads now or in the near future, thus they are going to focus on other business aspects for now.
Eventually one might want to buy a second GamePad if one so chooses whenever it is they come out, but that has nothing to do with how expensive the actual console/kit is, and you are not required to buy a second GamePad at all.
On a side note, Black Mesa comes out tomorrow guys, if you own Half-Life 1 then make sure you download this mod and play it - it's a complete reconstruction of the game from the ground up.