A craftsman of sufficient skill to make such bows is going to be exceedingly rare.... You're talking about a 10th-level or so fellow, who for whatever reason is willing to waste his time on crafting 900-gp bows for other people rather than conquering some small town all by himself or making his own little barony or something.
By 10th, he could have 13 ranks, +3 Skill Focus, +2 MW Artisan's Tools, +2 Intelligence maybe, and +2 from an assistant Aiding Another. Or maybe it's a 10th-level Wizard with high Intelligence and all those ranks, tools, and feat. You can't really have a bunch of assistants aiding another, because there's a limit to how much help additional people will be in the crafting of one item (and we're not talking about building a house or something, we're talking about crafting a 5-8 foot long collection of composite materials in a stave-like form).
You might be able to assume 2-3 assistants could help with the task, but it's still a rather high-level craftsman doing the bulk of the work.