http://www.harborfreight.com/heavy-d...ker-66488.html
Or a Dremel/side-grinder works well, but takes a bit of care.
I agree on not skimping on the chain - though that $45 one is
probably just fine for street/commuter-duty & a great deal if it's up-to-snuff. But wearing out a bit quicker is one thing, breaking a link is another. In my mind, it's somewhat of an unknown as to the actual quality (material/heat-treating - and I'm guessing it's made in China), and given the potential consequences of slinging a chain I'll stick with a top-notch established mfg. vs. saving ~$50 over 10~20k miles.
I'd recommend always replacing both sprox - you can't eyeball wear of just a few thousandths, and that's all it takes to wear out the chain much quicker.