I don't know about you, but I pay $6-8/hr to my babysitters, and feel lucky to get that rate. But I also use a local Parents Night Out to cover a significant number of hours as well as the fringe benefits.
The one I use is Head Over Heels Gymnastics in Emeryville, CA (http://www.hohgymnastics.com/). They have PNO every Friday night from 6-11 for $30 ($5 more if you sign up after noon on Friday; 2 or more kids are $25). Dinner is INCLUDED and it is for kids 4 and up. They always have pizza and, later, a movie. My son comes home exhausted, as they get free time in the Gym for quite a while, and they have this terrific pit of soft foam cubes to fall/jump into.
Kids don't have to stay till 11, but that is the movie time, and my kid, whose regular bedtime is 8:30, makes it till 11 every time.
Be sure to study the map on the website, as getting there is rather tricky.
Here are some other options. I haven't used them, but they do seem worthwhile:
JCC East Bay (I believe it is at the Berkeley location)
Monkey Business Camp (organic meals! but pricier)
Berkeley-Albany YMCA Kids' Night out (Berkeley location; you must be a full or Program member)
Color Me Mine, Alameda (pricier by the hour but could be fun and fill a need)
Studio Naga, Oakland (sounds interesting!)
http://www.studionaga.com/ Click on Kids' Programs, then Kids' Night Out
I also found one on the Peninsula: