I'm thinking that if the character is from a culture, or species, for whom Psionics is a regular thing, they can purchase it directly, as long as they abide by any other restrictions. For example, for Zhodani, I'd say that if they want a trained PSI of 9+, they'll also need to purchase a SOC of at least 10. I'm not sure how it would work for Droyne. Any thoughts on how to "balance" that against everything else? For Imperials, I think it would be fair to require that Psionics be a benefit that must be purchased to access, costing perhaps the same 25 points as a commission? That would give them access to purchase the PSI stat, and buying PSI skills will cut into available points for other skills, and stats.
The psionic is getting an edge that the other characters don't have. If they want PSI, they'll have to pay for it. That said, it only costs 14 pts to buy a PSI of 7. Take a look at the Very Quick Point-Buy. It's 84 points for all 6 stats of 7. For 7 stats of 7, that would be 98pts, not terribly onerous. Desired disciplines would need to be purchased at character creation, or additional work would be required in game play to add new disciplines. If you want a full complement of abilities, it's going to cost you. With 250 points, it's not cheap, but it's not crippling.
The point being that it should be doable, but not so easy that it doesn't make sense not to do so. If it's too easy, it becomes another TL12 cloth undershirt. Everyone would have to have it just to maintain parity.