| Krozber |
Sorry for the thread rez, but it's the first result when searching the topic, and the answer is incomplete.
As Mark Hoover suggested, the young template from the bestiary works. It specifically states, "You can also use this simple template to easily create a smaller variant of a monster."
If you flip to page 296, you will also see a sidebar about reducing hit dice. This says that you can de-power monsters using the monster advancement table, and if a monster loses 50% of it's original hit dice, it should probably reduce in size.
You could then use Jak's answer to find out the cost, if needed.
I would hesitate to use animated objects as a fix-all solution. If you look at their entry, you will see that they don't have the wisdom scores for following orders, and the text for the animate objects spell implies that the only thing you can tell them to do is attack. If you really need to shoehorn it in, it will work, but you will have to bend/break the rules.