Affiliate Marketing Secrets

Right now, I’m using a Micro Four Thirds camera called Olympus Pen PL2 (with a kit lens and a 45-150mm zoom lens) I’m pretty happy with the image quality right now but I’m thinking about upgrading for the greater range of advance features/option/controls and lens availability. However, I don’t plan on getting that many lenses in the foreseeable future in order to consider the D90’s internal AF motor over the D5100.
Along with this, I’m buying the cameras used. I could get the D5100’s body and kit lens, or get a D90’s body and about 100$ for another lens.
At the end of the day, I just want greater ranges of control and IQ improvements on the side. Which one should I consider? (My budget is stretched to about 500$. Please don’t suggest getting a D7000, which is out of my budget-range)