I am using 600VA APC ups with my Optoma HD20. This UPS saved my projecttor from power failurer several times.
You too can use the same.
You too can use the same.
I am assuming you never did use UPS with a desktop PC?
Just buy any microtek/APC PC UPS (Check with your local Inverter/UPS shopkeepers for latest models). Price will vary between 2-4K, I think. Any UPS which can provide safe switchover for PC will be able to provide safe switchover for projector, so don't worry. I think a 600VA UPS will do the job nicely.