D7k is highly overpriced due to supply shortages. D5100 has no in-built focus motor and comparing to D90 its sensor and viewfinder are smaller, big disadvantages in my opinion. Go for D90, a used one can be bought for much cheaper, and rest of the money can be invested in good lenses. I would recommend 50mm 1,8 (the bokeh of 1,4 is far better but the lens is also at least three times more expensive, 1,8 is one of the best budget lenses) and 55-200 4-5,6. Both lenses are quite inexpensive but the quality is actually quite good.
