Another good way to expand on this I think would be to tier out the credit costs a bit.
Example (all numbers are hypothetical):
Perk: Lightsabery Goodness
Legacy level 5: 1,000,000 credits
Legacy level 15: 750,000 credits
Legacy level 25: 500,000 credits
Legacy level 35: 250,000 credits
Legacy level 40/45 (does legacy even GO this high?): 100,000 credits
I suppose that would apply to more than the per-character perks, but still the same concept...