
Saethori |

The first step is to compare it to similar items.
As the items that provide air step are all of the temporary, limited variety, we instead look towards something that accomplishes what Air Walk is vaguely imitating; outright flight.
This gets us the Wings of Flying, which are infinite-use a day and provide a 60-foot fly speed, for the price of 54,000 gp. As these are strictly better than any hypothetical item that grants permanent Air Walk, no item that grants Air Walk should cost more than this.
The lesser version has a rather different flavor, provides a worse form of flight, and weighs more, but costs only 22,000 gp. Air Walk is slightly better than clumsy maneuverability, so this should be the minimum value.
I would price your boots of air-walking at much closer to 30,000 gp.

_Ozy_ |
I'm not so sure Air walk is uniformly worse than winged flight. You don't have to make fly checks for hovering, taking damage, or other maneuvers, though you can't go straight up or down either. Also, wings of flying can be entangled or impeded causing the flyer to fall.
Also, for a continuous item, the duration factor is x1.5, not x2.