The cost of a L1 Rancor seems to be 3250 credits.
It seems to be a glitch from inside the Research Lab. If you go to the item before the Rancor and look at the stats for that previous item (for me is the Wookiee wagon) then use the ‘next’ arrow, the Rancor training cost is shown. If you look at the info directly for the Rancor, or use the previous arrow to back into it, those stats are hidden. Continuing to use next shows the costs of the Shadow, Hunter, Rage and Krayt as 0.
Probably been noticed before... Kind of surprised me when I saw it.
Rebel Squad: Jedi_Falcons L10+ Perks: L38
Medals: ~70k Deka/o: 50/50 Jets: 5d/4f/4a