seemed like a good trial idea until I got onto the pricing page...

to get SSO, we'd have to start out with the 11$/user/month plan, in my current company(~1000 users) that would mean roughly 132 000$ a year making it a pretty tough sell.

But what is the value of something that actually helps users get answers faster? What is the cost of someone waiting around trying to find an answer? I can tell you from experience having implemented my fair share of content systems that:

1) You can always get them cheaper than the list price 2) If it works, the software pays for itself in less than a year

You can always get a tool for low-cost (or even free with open source). Having something that is already used by developers and has a good reputation makes it a pretty easy sale in my book.

This is where other solutions such as the Q&A plugin for Confluance have their place. The Q&A plugin for 1k users is $1000/year (on top of the $24k/year for the 1k users)... but that's a small fraction of the price for the enterprise cost.

... And lacking the integration with other systems, the enterprise version of SO (and for that matter, teams) really lacks a good price / integration / use pitch.

I would love to have something like this for a research group. But that is too steep a pricing!

At that scale it's likely you can negotiate a custom contract.

At my scale (<10 people), I can't. Are there any alternatives, open or closed source?

For 10 people you probably don't need the middle level, only the low one, which is $5/seat/month. There's also non-profit and educational pricing if you're associated with one of those. It's 50 cents/seat/month for the low level or $1.10/user/month for the middle one. They mentioned it on MSO. https://meta.stackoverflow.com/a/367590

Even at that scale you probably could ask - typically those companies value direct contact over "anonymous" online sales as they hope for longer term upselling opportunities once they have a name and phone number and give discount.