i got lucky the other day. i got a MS290 for under $200! its a great saw. go down to your local dealers and look at what they have for used saws. make sure that you look them over though. but you can find lots and lots of good deals used if you look, ive got both of my saws used for $200 and under and both are good reliable saws, but im lucky i have a great dealer who really cares about his customers and will do what he can to keep them happy, he always throws in some goodies when i buy stuff from him and goes out of his way to get me what i need. look around you would be surprised what you would find.
on a second note your going to want a saw with some power for firewood, nothing more aggrivating than standing there and waiting and waiting for your saw to get through the wood especially when you look up and see that pile of wood waiting for you. your deffinatly going to want to look into a saw bigger than 50cc. look at the MS260 MS290 and MS310 for a light little firewood saw, they have good power, good weight, and they are all good saws. if you really want to do some work i would suggest you pay the money and get a good saw if you plan to use it year after year and get something big over the 60cc mark. my Husky 365 makes chips out of big maple and oak with no problems, while i use my MS290 for the smaller stuff.
good luck in your search for a good saw, but make sure your really happy with what your getting or else you will regret it.
work smart, work safe.