You're welcome and I truly hope it helped a little. Vendors are probably a lot like any company in that they have a desired price but will go higher or much lower when they see future returns.
In the big scheme of things, 250 is low for most vendors so their costs (often and from my experience) are going to be much higher than they would for a 10k seat contract. They also add dozens or more of additional courses to justify their pricing.
I think your overall question is very relevant to our community in that we're seeing more and more consultants and subject matter experts create online versions of their expertise.
You could look at places that sell retail courses such as Lynda.com, AtomicLearning.com, VTC.com and view their single and multi-seat pricing to get an idea how they discount courses. Those are all technical, software training, but they're big like SkillSoft and might give you some additional insight into the retail, single course price and what it looks like with multiple seats.
I'd begin with your single, retail seat price and go from there. Also, you mentioned Articulate Online hosting. AO is awesome for hosting and course management, but has a per seat cost to you once you reach your plan's limit. However, someone like SkillSoft already owns their architecture so the costs of additional seats for them could be substantially less.