Well I'd try to get them cheep and find the ones that work but have bad batteries, replace the batteries, and them sell them at the local flea markets and Hamfests. However with units that small you need to get them REALLLLL cheep, like $3-$5 each.
a battery will run about $10-$14
The APC ES350 (200 watts) is going for $40.00
It's a crap shoot, good luck