I was in a very similar situation, so built this up 2nd through eBay and forum. bored of riding to work on roads to decided to play in the woods more.
Cost just short of £400 all in.
Charge Cooker frame and forks,
Six drivetrain/Deore Cranks
Alivo brakes
Shimano hubs on alex rims
Schwalbe marathon mondial 2.0 tyres (bombproof)
I have some mudguards to go on it in the bad weather, (from spa cycles) will use p-clips on the rear as no eyelets.
I’m guessing you could pick up a charge cooker frame and some steel forks cheap and swap you bits straight from your cotic.