Looking at probability travel in the Complete Psionics Handbook, it is almost exactly like a combination of astral caravan/astral traveler. So simply adapting those two should work.
I like the astral traveler/caravan progression. And write it up as a Su for the nonpsionic version (kind of like psionic dominate gets converted to Enslave)? It is kind of weird, though, that it would take so long to travel even a short distance on the Material if you took a "shortcut" through the astral. It really does seem meant for very long distance travel.
XPH said:Each successful check indicates that you are one step closer to your goal. To finally arrive at your location, you must succeed on six checks within a span of 12 days. (If you fail to make six successful checks within the first 12 days, you can continue to make one check per day until you get the requisite six successes within a span of 12 consecutive days).
When you successfully make the requisite number of checks, the journey ends, and you appear on your chosen plane within 10–1,000 (1d% × 10) miles of your intended destination on that plane.
OK...so we use bykov's astral traveler/caravan progression described above?
For the non-psionic version, should we spell out the power as a SLA, or something more simple like the following:
Astral Traveler (Sp): This functions exactly as the psionic power of the same name.
and...
Astral Caravan (Sp): This functions exactly as the psionic power of the same name, with augmentation.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.