Cheap alloy hardtail 29er frame in size S/XS (ideally one that will do singlespeed). Air shaft for your pike to the last travel possible.
Fast rolling tyres at high psi, seat set as low as possible.
Job done!
I’d want something cheap, well built and I’m guessing not too slack a HA.
Edit: I see you don’t want a dedicated jump bike. So, just build a hardtail and live with the limits that it’ll have for jumping over a proper jump bike.
A proper sized hardtail for you (480+mm reach) is very different to a jump bike with 430mm reach or similar.
Tbh, for the price of a decent ht frame, you’re not far off a complete dirt jump bike, £500-750 would get one.