looking for some advice.

[12:52MuLtiMediA]

Being a working musician for 13 years, I have in the past year or two started working with other musicians and bands alike photographing them live along with a few promo photo shoots, I want to take this even further and make this something I do for the rest of my life, instead of a hobby.
I use a Nikon d60 with a 18-55mm F/3.5 lens. I know working with lowlight with that Aperture is tough, knowing that of course, I have learned upgrading to an F/2.8 or faster would help me out.
My question is... on a budget what would be a decent lens.
I am looking into a Sigma 18-50mm f/2.8-4.5 DC OS HSM.

any input is more than appreciated.

Jason.
Btw, if you wanna see what I have photographed, you can find me on facebook, just look up 12:52 MuLtiMediA.

[inkista]

Your 18-55 isn't an f/3.5 lens. And the Sigma isn't an f/2.8.

Note that there are two f-numbers given for the maximum aperture. The lower one is the max. aperture at the wide end of the lens, the second numbers (usually higher) is for the tele end of the lens. So, with your 18-55, you've got a max. aperture of f/5.6 when you're zoomed all the way in to 55mm. The Sigma, when it's zoomed all the way in to 50mm has a max. aperture of f/4.5.

When people say you need an f/2.8 or faster lens, they mean through the entire focal length range. With zooms, this is very very expensive.

I'd recommend looking at the 50mm f/1.8. It won't autofocus on your camera, and it doesn't zoom but it's very inexpensive, and a great optical performer, and has a maximum aperture of f/1.8. Fast primes (lenses with fixed focal lengths) are most typically used as portrait lenses. It'll be sharper than your 18-55, and a lot faster, and it will teach you more about composition, ironically, by simplifying all your compositional choices down to "where do I stand?"

If you have to have autofocus, the AF-S 35/1.8 will work (or the much more expensive AF-S 50/1.4 or Sigma 30mm f/1.4 HSM), but be aware that 35mm still has a bit of barrel distortion, and it can make some portraits look a little funky. Depending on the type of band you're shooting, this might not be a bad thing , but better not to be forced into that look if you don't want it.

You'll probably also want to get bitten by the Strobist bug at some point.