I bought Nikon D3100 recently, can anyone suggest me cheap compatible wide angle lens?

Looking for Wide Angle Lens for my Nikon D3100

The 18-55mm VR it comes with is pretty wide. How much wider do you want to go? A wider lens that is any good will not be cheap.
A very, very wide lens is the Sigma 10mm f/2.8 EX DC HSM Fisheye Lens.

Superwide lenses are not cheap. Expect to spend $600-900 for a lens.

Your choices are the Nikon 10-24mm and the Sigma 8-16mm. The Tokina 11-16mm would be an excellent choice, but your camera will not be able to autofocus that lens as it does not have the required in-camera focus motor.

There's a tamron 10-24 for less than 500 and it will auto focus on a 3100 that's about the cheapest widest lens with a good zoom range you'll find.