Both "credits to energy" and "mercenaries, or neinzul railpods, or whatever" both sound really cool.
Not neccessarily at the same time, but like, as generic mechanics.
As for how much energy for a credit, 10 credits gets you 20 max energy, so I'd want to get AT LEAST 20 energy-right-now for a credit.
(Hmm, the Credit-Energy-Converter consumable is 5 -> 10, as many times as possible...I regularly have 100+ energy, sometimes as much as 200...I have never and probably would never use this consumable: 50 credits for a refill on energy is expensive and costs 7. The EnergyDrink consumable fills you to full--whatever that is--and costs 15 credits)