Unfortunately the FAMAS is one of those guns that's either very cheap (and cheaply made) or high end. Random off brand companies like Jing-Peng make them, but so did/does Tokyo Marui. The TM Famas' ran around $300 but they're sort of hard to find.
If you're looking for an M4, which is a lot easier to find at your price range, take a look at the G&G Combat Machine line. They sell for around $130-$150 and are very solid guns. They come with a hi-cap, battery and charger too. They also shoot about 350fps out of the box though. Finding a gun that shoots under $300 is going to be a little tough too and it might be easier to get a gun then downgrade it.