And I would do it proportional to the CUBE of the hit die increase.
That is, if you want to build a 22 HD Clay Golem (twice the normal HD), it would cost eight times as much.
EDIT: Ok, after looking at the Golems I see that it is not so simple.
Take the 22 HD Clay Golem. An 11 HD Clay Golem costs 60,000 g.p. including 30,000 for special ceremonial vestments. Those vestments need not be any more costly no matter how big the Golem you are making is. And while the Body clearly needs to be more expensive, the cost of the body is only 1500 g.p. It suits me that the ceremony is only proportional in cost to the square of the HD. So, purely as a suggestion, the cost of a 22 HD clay golem would be 30000 + 1500x8 + 28500x4 = 156000 g.p. (and 6240 xp), and the cost of a 33 HD clay golem would be 30000 + 1500x27 + 28500x9 = 327000 g.p. (and 13080 xp).
That should prevent 54 HD iron golems (yikes!) from roaming around your campaign world unexpectedly since 300000 gp (triple the usual cost) isn't impossible to come by for characters of high enough level to contemplate such things.