$250 for a mountain bike? Don't even bother - crap bikes really, really make life a whole lot less fun. However, if you were to budget $350-$400 you could pick up something pretty decent. Personally I'd be tempted to stay fully rigid, especially at the lower end of that price scale- the money would be better spent on a good frame, wheels and componentry than a cheap suspension fork. Definitely don't go full sus at this price. Unfortunately fully rigid entry level bikes are a bit of a rarity these days, which seems to have had the knock on effect of driving up the price of a budget bike which is suitable for offroading.
EDIT: I forgot to add, we (my wife and I) are looking at purchasing a new bike for her- entry level mountain bike for maximum flexibility (slicks if we start doing lots of road work etc), and are looking at spending AU$900-1000. Shopping around, that can get you a reasonable hardtail frame running Deore, with a half decent XC fork. That's pretty much the minimum I would recommend.