at the end of the rainbow
Said of something that is appealing but seemingly illusive or very hard to obtain. Yeah, I highly doubt you're going to find a raise at the end of the rainbow when you meet with your boss today.
at the end of the rainbow
used to refer to something much sought after but impossible to attain. This phrase refers to the story of a crock of gold supposedly to be found by anyone who succeeds in reaching the end of a rainbow.