I have a player (yeah, that guy) who would like to craft an item that allows Weapon Focus (several actually) to an item they would like to craft.
Having read the Paizo website several times, I'm still not sure.
Do the rules allow for this? If so, how do I calculate the cost of these enchantments?
Best Answer
RAW: No.
Generally, you want to check out the Crafting Magic Item rules to determine what can be created. The magic weapon crafting rules specify a bunch of things you can do (attack bonuses, special abilities, et cet.) but not feats. RAW this would be enough to say that PCs can't create magic items with feats.
Example - A Flaming Weapon
Intuitively, this makes sense. A magic weapon can burst into flames, giving it fire damage - this is a property of a weapon. A feat (like Weapon Focus) is a property of the character - they are particularly talented with a certain kind of weapon.
However - GM Shenanigans
There are a lot of magic items which look an awful lot like they give the user access to a feat. For example, the Disarming Blade closely imitates the Greater Disarm feat. The Dueling property gives a bonus to disarm attempts (among other things), and the weapon's unique property is a weaker version of the feat's other benefits.
Although the rules don't specify how to create these items, a GM may always create their own magic items. If you feel like this is a reasonable item for your character to have, by all means go ahead and create one for them. As far as the price goes, you will have to use your judgment. The Disarming Blade is slightly weaker than one feat, and costs +14,000 GP.
Personally, I would not allow a player to create such an item. They can already use enhancement bonuses to give additional attack/damage bonuses to their weapon; there is no need to shoehorn a feat into the weapon also.