Greenfield
Adventurer
The target DC is 15 for a normal item. Master Work has a craft DC of 20, according to the SRD.
By the book, you actually start by crafting a Warhammer, like any other. Then you craft the master work component as if it were a separate item.
Look under the Craft skill description.
As a solution to your challenge, in our campaign we tried to un-break Fabricate a bit by changing the way it works: Instead of simply providing all the labor instantly, it allows a craftsperson and a number of helpers (1 per 3 caster levels) to craft faster, doing a week's worth of work in a single day. The caster has to be included in the group, either as the master craftsperson or as a helper.
This allows the spell to account for things like master worked artisan's tools, Aid Another and other circumstance bonuses (and penalties) that may apply. It also keeps the guilds from going on strike whenever there's a high level caster in town.
But this version of Fabricate may help you address the issue. At that point you're producing results measured in silver pieces instead of coppers, and your required skill checks drop sharply. A target DC of 60, with a skill check to match, would produce 3600 SP in progress, which translates to 360 GP.
With or without this, consider circumstance bonuses such as "Crafted during the Summer Solstice", which means a long, long work day. Go far enough north (beyond the Arctic Circle) and you can get several months of direct sunlight on your project, and thus make the project possible with sane, unenhanced skill modifiers.
By the book, you actually start by crafting a Warhammer, like any other. Then you craft the master work component as if it were a separate item.
Look under the Craft skill description.
As a solution to your challenge, in our campaign we tried to un-break Fabricate a bit by changing the way it works: Instead of simply providing all the labor instantly, it allows a craftsperson and a number of helpers (1 per 3 caster levels) to craft faster, doing a week's worth of work in a single day. The caster has to be included in the group, either as the master craftsperson or as a helper.
This allows the spell to account for things like master worked artisan's tools, Aid Another and other circumstance bonuses (and penalties) that may apply. It also keeps the guilds from going on strike whenever there's a high level caster in town.

But this version of Fabricate may help you address the issue. At that point you're producing results measured in silver pieces instead of coppers, and your required skill checks drop sharply. A target DC of 60, with a skill check to match, would produce 3600 SP in progress, which translates to 360 GP.
With or without this, consider circumstance bonuses such as "Crafted during the Summer Solstice", which means a long, long work day. Go far enough north (beyond the Arctic Circle) and you can get several months of direct sunlight on your project, and thus make the project possible with sane, unenhanced skill modifiers.