You will probably need something that is about 12u+ in a server rack, and have all the electricity run into that. You are looking at an investment of a minimum of $8000 US
To power 11 PCs you would need a commercial UPS that will have a spereate rack of batteris for it.
This in no way is an "off the shelf" application, and in all likliness will cost more then 11 850va UPS units.
Newegg has hem on sale regularly. I would suggest looking there, plus they have volume discounts.
I looked into something similar in the past. It was much cheaper all around to buy individual ups for each computer. A central unit would require an electrical contractor to put in additional wiring on top of the cost of the unit itself..