I have dilemma what camera is better Nikon D5100 or D90. The first one is newer but the second one has lens servo ("screwdriver") motor. My question is: can I save some money overall with the more expensive camera, by buying lenses without lens-based AF motors?
If money is the only consideration and if you plan to buy many lenses, I'm sure the answer is yes. The newer AF-S lenses are more expensive than the AF-D predecessors, or the AF lenses before those.
If price is the only consideration, you might forego AF altogether and get some old MF Nikkors. They're often cheaper still.
I have trouble endorsing the direction this thought process leads, though. AF-S lenses often offer more than just internal motors: better optics are pretty standard. I while back I pulled out an old 35-80mm f4-5.6 AF-D "kit" lens and shot with it a little on my D300 and was amazed at how poor the optical quality of it was as compared to the 18-55mm AF-S "kit" lens. It wasn't bad, but the 18-55 was clearly better. I'm sure that there are many great AF-D lenses, but I suggest that you'll really need to do your research to be sure you're getting something worthwhile.
Of course, the AF-S lenses offer two other great benefits, too: generally faster AF, and much quieter AF.