I guess you're still missing the idea that education is THE use case for OpenSim.
Say you've got a class of 20 students and you spend a few hours a week on a region, doing math simulations or a biology simulation or whatever.
With the discount, Second Life would cost $500 to setup and $150 a month to run. Plus, once you built everything up, you wouldn't be able to save it.
You wouldn't be able to have young kids on the region, and older students would have their own avatars, and be able to go anywhere they wanted to in Second Life.
After you and your students -- or the developers you hired -- build your simulation, you wouldn't be able to make a backup of it and share it with other educators in your district or outside of it.
And Second Life's large user base is of no benefit to your students. In fact, that user base is more of a potential threat.
Now consider OpenSim. You could rent the same region for around $50 from a professional hosting provider, a lot less from Kitely, and zero if you run a mini-grid on a classroom computer and local network using something like Sim-on-a-Stick or New World Studio. Plus, with a local network -- no connectivity-related lag!
You would create the accounts for your students, and you could close the accounts for your students once they're out of your class, so they can't come back next year and annoy people.
Once you build everything, you can save it as an OAR file and share it with all the other teachers in your district, email it to friends, post it online. Or just keep it as a backup for next year.
You can have multiple setups that you save as OAR files, and just swap them in. Or make backups at different stages of your build, so you can go back easily if you mess something up.
If you turn on hypergrid connectivity, you could travel out to other grids to network with other educators, or to get content, or do do field trips to virtual museums. Or you could turn off hypergrid and keep your minigrid completely private and your students totally safe.
The reason that I'm comparing SL and OpenSim here is specifically because for educators, the advantages of SL (community) are moot, and the advantages of OpenSim (backups, privacy and control) are vital.
And the fact that they use the same viewers, the same building tools, and can use the same content if it's exported correctly -- that's a big plus, as well.