In that price range, look for something used.
31 lbs is heavy for an xc hardtail (which is what those are trying to be) but a few upgrades down the road can drop that number quite a bit. I'd still recommend looking for something lightly used in that price range though, as you could likely pick up a bike that msrp's in the 800-1000 range, which will be a HUGE step up in component quality - most importantly the fork and wheels. The forks on the bikes you posted are damn near useless.
The fisher looks to be the nicest of the 3, though