KD - are you installing retrofit windows or new fin nailed windows? You mentioned you have the windows already? You could probably hire a handyman to install it. Windows installations are pretty simple (especially retrofit windows). I have done the Windows at my parent's and sister's houses. Don't remove your window. Let the installer remove it. It doesn't take long to remove the window. Ask the installer to make sure your replacement window will work. That way, if they remove the window and realize they can fit it, it becomes their problem and not yours. If you remove the window, and you discover problems, the installer can decide not to install the new window, and you'll be stuck with a hole in the wall.
BTW - I had my windows "professionally" installed. The only reason why I had them professionally installed was because I had a bay window and a garden window. The bay window was really heavy and took 6 big guys who struggle to lift it. I wasn't really happy with the installers. They seem to slap on the windows and trim as fast as possible. There were no pride in workmanship.
Integrity Windows (located in Davis) did my neighbor's window. Their craftmanship was top notch. However, I don't know how much they charge - but I bet it wasn't cheap.