A new lens or even a new camera will not improve your skills. You'll be risking getting "took." Anyone selling the higher end lens at $100 is either trying to dump it on an unsuspecting person who won't test it or examine it... or the person is mighty dumb, which i strongly doubt. Or it must really look like it's been trashed and you haven't even SEEN it.
Why won't a new lens or a new camera improve your skills? Because YOU operate the camera and control the lens settings, and whatever you're doing wrong is exactly what you'll continue doing with a new camera or lens.
Save your money. Learn to use your current gear; there is no reason (except your lack of skills) that will prevent you from getting excellent exposures with your kit lens, which is a mighty good and versatile lens. And, for heaven sake, don't become a lens or gadget collector! However, it's your decisions. So, good luck and best wishes.