First: Not all HU superpowers are really applicable as talents. Most are simply better off as being Morphus Traits. Remember, you can customise morphus traits as much as talents. Ex. Spd, PS, Healing factor and the like are better off being traits than talents.
For some, like Super Enegery Expulsion, I've found the easiest way is to use Darkblast rules, only change the element involved (Shadow to fire, cold, electricity, ect).
Some, even minor powers, are simply far too powerful to be converted wholely. Remember the distinctly different feel of the games. Some powers with nightbane wouldn't work so good. What use is a nightbane with Space Native? there are no nightlords in space. And if you change the campaign setting that much, I cna't help you
![Razz :P](./images/smilies/tongue.gif)
but no, there should be no set "cost" for minor or majors. I'd charge far more PPE for Warp Sound than I would for, say, Nightvision.
And also remember the key difference here: A mutant at most will have 1-2 majors and 1-3 minors. or at most, 5 powers, sometimes as few as 3.
Nightbane can have up to 35 talents. if you just convert superpowers straight over, without some heavy PPE costs, it's just plain rediculous and unbalancing.