[RPG] Do rules exist for creating artefacts

So far as I know, animated objects are the result of an animated object spell, nothing else. Hiring an NPC to cast animate objects and then permanency would cost 16,540 gp minimum (caster level 14th for the casting of permanency on animate object; at that CL you could get a Huge one).

Crafting a Construct by the Craft Construct rules would result in a creature not vulnerable, as a permanent animate object is, to dispel magic, which is a rather huge advantage. On the other hand, it takes longer to set up (the whole crafting time), not to mention the Craft Construct feat itself, so it perhaps makes more sense to compare it to other Constructs that you can craft. It’s better than a Flesh Golem (20,000 gp) most likely, but not as good as a Clay Golem (40,000 gp). I’d probably put it around 25,000 gp then, base cost.

Although I don't remember the direct sources, there have been a few books out there for d20 based games that discuss what I will call 'legacy items'. These items level over time with the players. They must put in the time with the item and in some cases something else, such as gold for ingredients, a sacrifice of some kind, or as a reward (of sorts) for a momentous occasion. There is also, generally, a minimum level for each enhancement level equivalent on the item. This approach could work for players with magic tomes and such as well.

I'll give an example to help clarify what I mean:

A player wants to play a samurai, and as part of his story, he want a blade that's been handed down through his family's lineage for generation. It has great rumors that the strongest heroes of the family have been able to harness the power of lightning through it.

It begins as a masterwork katana. Functionally, this is all it is at this level. At level 3, the samurai gets 1,000 gold in incenses, food, and other sacrifices, and offers them to his ancestors, hoping to please them. They 'are pleased' by the sacrifice, and thus afford the weapon a +1 bonus.

A year goes by, and although he continues to honor his ancestors it is more time for him to show his own heroism in order to awaken his blade. This comes in the form of killing a tyrant in the midst of a thunder storm. He is now a level 9 character, and his act of heroism has allowed his katana to gain the lightning burst ability.

This gives a good idea on how to approach it. Add powers to the item as the wielder unlocks the power. Use the level suggestions in the Ultimate Magic book as a reference for when they could reasonably gain that power, while adjusting for the powers that are already there. Simply give them the power instead of a new magic item in the same place. It gives that one item a much more personal feel anyway, and players tend to love that one choice item that level with them.