If it's early March, you might see something go lower. If it's mid-late March, my guess would be slim to none that you would see something less than $300 a person. That's prime spring break time so supply and demand will fuel the prices. It's peak season in WDW from mid-Feb to Mid April so prices are higher at that time ofyear.
dudspizza will tell you to hold out for low $200s on Sun Country. Personally, I don't know if in mid-late March, low $200s will happen. But I don't go in March, so who am I to really say?
I guess the answer is a firm maybe. I guess the best advice is to watch the fares daily, multiple times a day, and if it drops to a price you can live with, jump on it.
If you haven't checked Sun Country or Air Tran, and feel ok going with one of those, do that. Sometimes they will have some great sales if you hit them just right.