Katie,
Try Priceline (
www.priceline.com) and select "Flights". Put in your dates.
Right now I can see an "Express Deal" for $165, with some selection of times. The risk will be whether you get a non-stop or not. With the stop they say a maximum layover of 3 hours. That bites quite a bit into a 3 or 4 day trip, but might work for you if the money is worth losing the time.