You seem somewhat misinformed,
if you want to get him at level 11 you can. You just need to acquire him on a level 50 first and then unlock him via Character Perks. And THAT is the real issue, the unlock for HK-51 so I can give him to my level 31 Operative? 1,000,000 credits. OUCH. I think I'll go with the secondary payment for the perk, which is 350 CC for unlocking him for a lowbie.
Suggestion BW: Please make the legacy unlock for HK-51 Legacy wide, having to spend 1M credits/350 CC for any lowbie I want him on is ridiculously expensive. I want HK-51 on my Merc, Gunslinger, Vanguard, Operative and Shadow. 5x350 CC = 1750 CCs, that's way too expensive guys!
Well it's kind a harsh to be THAT expensive!, and still you can't get him for the first character!, only at level 50!...