The August One Dollar book from Orbit is Night Shift, by Lilith Saintcrow. This is the first in her Jill Kismet series, the latest of which is now available for pre-order: Redemption Alley ($6.39).
Book Description
Not everyone can take on the things that go bump in the night.
Not everyone tries.
But Jill Kismet is not just anyone.
She's a Hunter, trained by the best - and in over her head.
Welcome to the night shift...
I don't have the links, but this should also be available in other ebookstores (links above are for the Kindle version) for a dollar (although some sources never did reach a dollar last month; I'm not sure Fictionwise ever discounted last month's selection).