You do get what you pay for at this level ,if youre just ticking the bullshit box by fitting a sequential gearbox then your stuck with agricultural units like these ,the quaife boxes still use a Male/female dog gear that makes re-builds expensive as its the gear that wears out,the Elite at least uses Dog rings and has the benefit of "Drop Gears" to give final drive ratios without the need to change your diff but the change is slow and then you need a bell housing etc...
If youre thinking of competition you must also remember most championships take a dim view of sequential boxes as a retro fit and boost you up at least 1 class if they let you use one at all !