Honestly, $5kNZD (~£2k) will get you a really nice bike that should take you to very enthusiastic amateur; if you are doing significant jumps/drops than you will know what you need and spend accordingly.

A $5k bike is not extreme by any stretch; and the NZ tax also hits. I have seen $14k (~£6k) in my local bike shop, non-electric mtb.

Note: I mountain bike regularly and my bike cost me $5kNZD 12 years ago...I mainly ride grade 2/3 tracks these days with the occasional grade 4. Not an authority on mountain biking, but I have a bit of experience in bike costs and what you get for your money.

I've found mountains to be very challenging to pedal and steer. Rocks in the other hand

Seen enough of people looking down on anything below a few thousand. Oh no my bike weighs a kg extra. So what, I can still cycle along the same coastal path as you at a slightly lower speed. I don't care how long it takes.

More variable but some cheaper bikes are more durable too, usually when the expensive one is as light as possible it is sacrificing durability to do it. But that does depend on what is being called cheaper too, as it seems like £80-800 is all considered cheap to these people.

Generally speaking, the more advanced the riding you're doing is, the more an expensive bike will help you.

Road bikes also get the same comments. I have a hybrid/trekking bike so I can annoy both sides. But realistically I use my bike to get to places along paths in the UK, I don't need to do jumps but I do need something that can manage shit road surfaces, dirt and gravel. Even light mud is fine with 700x37 tyres. I could use wider tyres for winter if I really wanted to use some of the muddier paths but there isn't much need to.