That definitely makes me understand that the easier route is to buy a new kit.
"Plain" developer is not to be found anywhere outside kits.
In the few places where I found E-6 developer not in kit, it always was of the starter-replenisher kind, and if I understand correctly in order to use it "one-shot" with the Jobo I should buy both, and that gives a too large and too expensive amount of first developer to buy. First Developer is the most perishable should be the one to be bought in smaller quantities.
Thanks for the your help.