While we have blogged about it before, people still spend all their budget on a camera and feel forced to buy one with a kit lens. This is completely the wrong approach. Instead, you must save enough to afford a good lens. As a ballpark figure, expect to pay 50% to 200% of cost of the camera for a quality lens. This is more true than ever given how fast pixel resolutions have increased.
With APS-C cameras now pushing 24 megapixels, kit-lens defects which visible at 12 MP already are very destructive. While doing the ISO test for the upcoming Nikon D7100 review which features a 24 MP sensor without anti-alias filter, we also took the time to shoot the ISO 100 samples with the kit Nikkor DX 18-105mm F/3.5-5.6G. The entire set of ISO sensitivities was shot using the Nikkor DX AF-S 17-55mm F/2.8G.
On the left we have a crop from near the center and one from near the edge using the high-end 17-55mm F/2.8. On the right, the same crops from the 18-105mm F/3.5-5.6. Know that both images are completely in focus and this is the best of 9 test shots taken with each lens. This is shot at F/5.6, so the kit lens can be stopped down to improve things somewhat but this comes at the detriment of light, shutter-speeds or image quality if one were to compensate by raising the ISO.
The 17-55mm F/2.8 costs around $2000 USD, while the 18-105mm costs around $400 alone. The Nikon D7100 goes for around $1200. With a limited budget, it is preferable to lower the quality of the camera to afford a better lens. In fact, this is a better investment as good lenses keep their value a long time while cameras depreciate quickly.