Most aluminium hardtail frames are okay at this price, albeit not always as light or as stiff as you'd like and tubing is plain gauge, sometimes with one butted tube. A fully-butted frame would be better and lighter, but would require component cuts elsewhere.
It's the fork that bears the brunt of budget limitations. Given an acceptable frame though, the fork has the biggest impact on overall riding performance. The hyperactive rebound of most cheap forks makes them horrible on armoured singletrack, and although you won't notice the difference between an Alivio and an Altus rear mech when it's covered in mud halfway round a local route, you'll feel a cheap fork's limitations every time you ride.
Cable discs are a small improvement over V-brakes but weigh and cost more, so V-brakes and disc hubs are a cheaper option. Upgrading is still easy, but it frees up money for a better fork.