Used 4x4 side by side ATV

[Diehard]

Ok so now I'll be looking for a "mule" type ATV, but not right away unless its a "steal".  I don't know a lot, but I know I would like  it to have 4 WD, a bed to haul stuff. Engine size, 500cc? Must be a side by side so I can drive it.
Any comments ideas or suggestions will be welcomed. Thanks.