Be sure to have the gas fireplace vented to the outside. In general, venting such a device inside is not a good idea. Here is a good read on the subject:
http://www.greenbuildingadvisor.com/...long-your-home.
I have to question the thought that you might have the thing running for a good part of the winter (the worry about expense suggests this). In general, any fireplace is not a great way to provide heat to a house. They are more for decorative purposes. If you are concerned about comfort and cost through a NE winter, you should be thinking about making the house superinsulated and tight.