The first dirtjumping bike i got when i first got into dirtjumping was the kona scrap and for a starter bike, it was great. Although i wouldn't usually advise to get a kona, it did the job and was a good price(less than a grand)
in my opinion id go for a p.1 p.1s are really good bikes espeacially for the money look for reviews on them. also go to ur local bike store and if theres a bike that you like ask if you can demo it
the money you put into the havoc getting it singlespeed and a rear brake it'll cost you the same as the district SS in the end. Just save up a bit more cash and get a bike that'll suit your needs. plus the devinci frames are gauranteed for life. any cracks, bends, whatever they'll replace it.