Build up out of new/used parts.
I’ve just done this: a 10 speed Deore groupset from Merlin for £226 (brakes, rotors, BB, chainset, shifters, mechs, cassette, chain & cables=BARGAIN!) then most of the rest of it from teh classifieds on here. Also check out Pinkbike.com for the buy/sell there.
You can make/buy a stonking bike from £800 if you don’t mind that’s not all new. A new bike for that much is going to have comprimises unfortunately, probably in the form of a mediocre fork and low end drivetrain which are both expensive to upgrade.
I really like steel for a hardtail, I personally have a Dialled Prince Albert (mk1) set up as a rigid 69er. I used to have a mk2 set up with a Revelation, it was an amazing bike to ride! PA frames come up on here regularly and not for too much, got my second one for £80 with a headset, post and clamp 😀