Umm you might get lucky and find one used for $300 but they usually go for aroung $550-$600. Also they do not shoot 3 1/2 only 2 3/4 and 3". 6 shot mag and sling with synthetic stocks and has a nifty 18' bbl. Here is the link to Rems website.
http://www.remington.com/firearms/shotguns/870MRMAG.HTM
Why am I sittin here on this stupid PC when I could be huntin'