I want to get a power adapter for my nikon d3100.cheapish way to do this?

As far as I can see
I could get a battery grip with 2 batteries,
or I could buy an adapter for an adapter for an arm and a leg.
any suggestions?
by cheap I mean under ~$30

Added (1). Alright, thanks I'm only a hobbyist photographer, and I only wanted it for taking timelapses, so I just wondered if I could get away with something for cheap that I had been missing.

I don't think you'll find what you want for that money. My precaution is don't buy an off brand of either one. Too many horror stories out there about products that ruin cameras when they're not specifically designed for a particular camera. A D3100 is too much camera for you to risk that, don't you agree?

The battery grip is totally portable and adds some stability when using long lenses hand held.

The AC adapter will require you to have a wire running from your camera to the mains. Okay when shooting in the studio, but not practical

Nikon does not make a battery grip for the D3100 and a second battery will cost you more than your $30 budget ($41). The AC adapter costs nearly $120. How did you arrive at this $30 figure for your budget?