Nikon D5100 18-250 lens?

Please suggest me a good low price 18-250 lens for Nikon D5100, i have not much idea about the DSLR cameras…

I'd think twice about that.

Tamron do an 18-270mm, but you have two problems;

a) Such lenses are heavy and/or bulky - having one hanging around your neck for long periods is extremely uncomfortable.

b) The longer the zoom, the more optical compromises have to be made. Optical performance leaves much to be desired.

Both problems can be remedied by supplementing the 18-55mm, which should've been your first purchase, with something in the 55-200mm range (the spare lens can fit into a pocket).

If you're just starting out, body and 18-55mm will be perfectly adequate - and don't fixate on Nikon just yet.

The Nikon AF-S 18-200mm is a far better lens. Like any super zoom lens, it has a slight amount of distortion and softness when compared to the combination of the 18-55mm and 55-200mm. However, at f/8, these issues go away, so consider it a daylight lens.

And since all superzooms start to experience issues, the more powerful you go - the worse the lens. In that regard, the 18-200 is a more moderate lens, and will not have the issues the higher power zooms have.

For the express purpose of travel and vacation - you may be willing to trade off the need to use this lens at f/8 vs the convenience of only carrying one lens.

Here is a comparison between the 18-55mm/55-200mm and the 18-200mm lenses (I own - or at least used to own all three lenses):

http://www.althephoto.com/lenses/super-zooms.php

I own the Tamron 18-270mm PZD lens, and it works just fine as a walking around lens.
http://www.beachcamera.com/shop/product.aspx?sku=TM18270VCNAPZD

I like the convenience of not changing lenses in the field.

Here is a competitively priced list from a very reputable seller. If you can find another that's way below that, be extremely suspicious.

http://www.bhphotovideo.com/...4108103566

Yes, the longer the zoom range, the poorer the lens is optically. Blame that on Physics.

I'd suggest getting the 18-55 & 55-200mm VR lens. You can find them refurbished at reasonable prices.
Low price for a 18-250 lens isn't going to happen.

The only 18-250mm lens I know of is the Sigma 18-250mm F3.5-6.3 DC HSM.
I have no idea where in India you might find one, but make sure you purchase it in Nikon mount because it is also available in Canon, Pentax and Sony mounts which will not work with your camera.

It's not a bad lens, especially for the price and gets reasonable reviews:
http://www.ephotozine.com/article/sigma-18-250mm-f-3-5-6-3-dc-macro-os-hsm-lens-review-19470
http://www.dpreview.com/...-hsm-macro

The Nikon 18-200mm VR is a much better, sharper lens, but also significantly more expensive.

Assuming your camera came with the standard 18-55mm lens, you might be better off with a Nikon 55-300mm VR lens. Not only will that cost you less, it will give you slightly more range and be sharper. Of course you will need to changes lenses occasionally, but that's kind of the point of a DSLR camera.