
Mark Hoover |

How would one price size reduction and HD decrease for specific golems?
I have the idea of a character recreating his son as a flesh golem.
I would love to be a player or an NPC in that game:
This is MADNESS BBT! You're letting your grief dictate your actions... You are a man of SCIENCE! What you propose... is BLASPHEMY!
Ok, firstly, I'd suggest using a homonculus, not a flesh golem. If that's not ok, I'd say use a sliding scale based on the CR3 wax golem costing 14k and the CR7 flesh golem costing 20.5k
Incidentally; how powerful do you want Son of Reanimator to be? And why not make him a Zombie Lord?

Jak the Looney Alchemist |

bbt This is where I'd start
"This section provides guidelines for those seeking to calculate the costs of crafting their own constructs. As a rough guideline, a construct’s price is equal to its challenge rating squared, then multiplied by 500 gp. Constructs with a fractional CR rating base their price on that fraction of 500 gp. For example, a CR 1/2 construct has a price of 250 gp. The cost of magical supplies for the Craft Construct feat is half this price, with the construct taking 1 day to create per 1,000 gp of the construct’s base price. Some constructs, particularly golems, have additional raw material costs that must be paid in full, regardless of whether the creator possesses the Craft Construct feat. Raw materials typically cost somewhere between 5% and 10% of the construct’s base price.
Constructs with multiple special abilities cost more to create. The first special ability is included in the construct’s base cost. The next two special abilities increase the calculated price by +1/2 CR per ability. Thereafter, any additional special abilities add +1 CR per ability. Examples of special abilities include having a higher DR value than a typical construct of its CR (above DR 5 for CRs 1–8, above DR 10 for CR 9+), monster statistics that exceed those recommended for the construct’s CR, the standard golem immunity to magic, DR or hardness that can’t be overcome by all adamantine weapons, ability to be fully healed by a single spell, and most special attacks and special qualities.
Particularly powerful special abilities, such as an iron golem’s exceptionally high attack bonus, count as two lesser abilities. Animated objects are a special case—their base price is not increased by any abilities paid for with Construction Points, since these abilities are already factored into an Animated Object’s CR. In addition, golems and homunculi created with extra Hit Dice, the advanced template, or shield guardian abilities should all be priced as described in the Pathfinder Roleplaying Game Bestiary, rather than by adjusting pricing for their new CR.
Abilities that weaken or potentially place a construct at a disadvantage rarely reduce the construct’s price. An exception is the berserk ability. Constructs that have a chance of going berserk receive –1 CR adjustment to their calculated price if control can be reestablished (like a flesh golem) or –2 CR adjustment for permanent loss of control (like a clay golem). The following is an example of the calculated costs for creating a stone golem (CR 11). A stone golem’s special abilities are golem immunity to magic, full healing from transmute mud to rock, a high to-hit bonus (+22 vs. the +19 typical for CR 11), and the ability to slow its foes. Further, since its spell vulnerabilities are not tied to common spells or effects, its immunity to magic cost is doubled, giving the stone golem a total of 5 special abilities. The first special ability doesn’t affect the cost, the next two increase the cost by +1/2 CR each, and the final two each increase the cost by +1 CR individually, making its effective CR for pricing equal to 14. This produces a calculated price of 98,000 gp, rounded up to an even 100,000 gp.
When designing a new construct, keep in mind that the above pricing formula only serves as a guideline. As with magic items, construct pricing remains more art than science, and like magic items, compare new constructs to existing ones for guidance. If you’re not sure, err on the side of a higher price."
Probably should have just done a link. Check out your ultimate magic.
Edit: Shrinking a golem is one of the few times I could definitely see lowering the cost in relation to cr. Considering that size influences quite a things for them. To drop a golem's size is to plummet its combat effectiveness and overall survivability.

Jak the Looney Alchemist |

You are effectively creating a new creature either way at least until someone can find some rules for making mini golems. I have not found any. I've looked. Wanted a mini iron golem. This is the best I've found so far.
Assuming medium size for an adult human. I'd drop the young template on it. That's going to affect pretty much everything but con which is still affected because golems get bonus hp factored in on size. So you drop the cr. Which then drops the price from 10500 to 9000.

Mark Hoover |

Mini-Golem... H O M O N C U L U S!
Switch some powers around. Jak is right; there's no way to just simply reduce the size of your golem as a player. I looked as well for a 3.5 character a few years ago (3rd party PrC called a puppetmaster. I was a lady wizard, horribly withdrawn like a child; all her golems were her toys) and recently went hunting again.
But I had a lot of luck with my GM if I just mixed and matched like building action figures with a homonculus. I had quadrapeds, flying pixies, even fleshy ones I passed off as children; all as size Small and scaling up and down from the 2050 price tag off the homonculus.

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.