Originally Posted by Robotech
At that price, and with that criteria, your best bet may be to get a Tippmann A5 or X7 and get one of the Tacamo Dmag magazine conversion kits.
Durable markers, inexpensive mags (though you have to buy them in bulk), runs on CO2 or HPA...and the right price range.
Or buy one already set up used, for $400 you should be able to get an a5/x7 with tacamo and a handful of mags used... maybe even a few extras. There's a good facebook bst set up for only magfed paintball items