I'm trying to determine the cost of a Boots of Striding, which offers a +10 enhancement bonus to base speed, while discarding the Springing part, which grants a +5 competence bonus to Acrobatic (jump) checks. The listed cost of such boots are 5,500 gp.
Normally, when adding a second ability to a magic item, you multiply the lower item's cost by 1.5. A +5 competence bonus to a skill normally costs 2,500 gp, so it seems likely that it's the speed bonus that carries the lower cost. So, if the Striding ability cost 2,000 gp, multiplied by 1.5 equals 3,000; added to the Springing ability's 2,500 gp results in the full item's cost of 5,500 gp. Does 2,000 gp for a +10 base speed increase seem correct?
How much might the cost of additional speed increases for an item be calculated?