I use an RS 1500 VA on my G5 DP.
but you may consider it pricey.
i wouldn't get anything smaller than an XS 900 which is what i have for my daughters G5 iMac.
APC has a helper at APC selector and you can get an idea of their recommendations. then google around for best price..
just remember, batteries are included, they are heavy when it comes to shipping. so after you find best price, print it and ask a local retailer if they will match the price.

luck

don't forget the data. that's the expensive part.
I have migrated hard drives for over 20+ years.
the oldest file on my G5 originated on an apple lle floppy

it's a VERY worthwhile investment.

If all you want is maybe 10 minutes of run-time so you can finish something and shut down gracefully, you don't need anything bigger than 800. As the other guys sed, tho' , if you leave it on unattended or want to keep going a while, then 1000-1500 is a good idea. APC is my favorite, too, although I prefer Powerware for UPS's that include transformers (APC calls it AVR) because I've had too many Back-UPS Pro's where the AVR circuitry went bad.

Putting a printer into a UPS is not recommended. UPS of the desktop size are not built for the kind of current draw involved in laser printing. UPS's aren't meant for heaters or motors, and a fuser is nothing more than a special-purpose heating element. Even an inkjet (while printing) will run the battery down faster than most peripherals. As jeffeyer alluded to, the manuals say no printers at all. Tho' a small inkjet might not cause damage aside from using up the power quickly, I wouldn't try it.

If you need printing through outages, APC will direct you to a power consultant in your area. They can tell you what solutions are possible, but you'd probably be looking at a busine$$-class unit.