I have heard a lot of good things about APC's UPS products. I saw one for as low as $85 that'll give you about 1 hour and 23 minutes worth of back up time. I believe APC UPS's are what we use in the office.  Here's the website:

http://www.apc.com/products/

Also, you can try taking a look at UPS's from CyberPower. Here's their website:

http://www.cellwaveguard.com/cyberpower.html