How much is a 3-6 hr UPS?

The price becomes very unreasonable after 1 hour UPS...

I got a one hour APC UPS for 3500/- last year at bestel - it was an offer. 650 KVA - 20 minutes for old desktop, 30 min for modern desktops, 55 min to 1 hour for 21" TV or 1hr20min Laptop.

What if one lines them up in series or parallel with one hour UPS of the highest power rating that can serve your equipment? Can they serve the intended 6 hours ???