As a little backstory, I wanted this because I'm making a fighter who is focussed on grappling. The problem is that any grapples with a foe more than one size larger than you automatically fail. In case he ever ran into a Huge, Gargantuan or Colossal foe, he'd lose his typical fighting style. Which is why I figured a Ring of Giant Size would be nice, so he could go up against those foes. But in my calculations I forgot that the size you grow to depends on the level of the caster. A 13th level Wu Jen could only make a ring to grow to Huge. To grow to Gargantuan the Wu Jen would need to be at least 16th level (so the ring would cost 120,960 gp) and to grow to Colossal the Wu Jen would need to be at least 19th level (so the ring would cost 144,216 gp). But a more cost effective way to get around it, is to get a Ring of Expansion. That could be used to grow to Huge and would only cost 21,600 gp. And I'd just have to hope I never ran across a Colossal enemy.