What is the difference between these two lenses?
There's a Nikon 70-300mm lens
http://www.nikonusa.com/...IF-ED.html
and a 55-300mm lens
http://www.nikonusa.com/...ED-VR.html
why is the 55-300 $190 cheaper?
what are the pros and cons of each?
The 55-300 mm lens is a new lens and is really designed to replace the older 55-200 mm lens and compete with the Canon 55-250 mm lens. Both are designed for use on entry level cameras with cropped APS-C sensors.
The 70-300 mm is for both ASP-C and full frame cameras. It covers a larger area at the focal plane, thus costs more
I would consider Nikon 55-300mm f/4.5-5.6G ED VR AF-S DX NIKKOR Lens for Nikon Digital SLR
5.5x Telephoto Zoom lens
Nikon VR II Image Stabilization; Tripod Detection Mode
HRI (High Refractive Index) Lens Element
2 Extra-low Dispersion (ED) Elements