Which crankset for a Giant Rapid 2?

The stock crankset that came with the bike I forgot which brand it is but it comes with the 3 gears or sprocket not sure the terminology for it but I never use the smallest gear (in the front of course) and I would like to upgrade to those cranksets that has only the two gears. I'm looking for the cheapest but reliable one. I've seen alot of them but I'm not knowledgeable about them. Can someone help me? Thanks