I normally just lurk, but I thought it was important to contribute this one since I know it personally.
For my program, my stipend is only about ~$1800/month for the 9 month period as well. However, our department also gets a "fellowship" tacked onto that which ends up making it around ~$2400/month. In addition, if you're talking about the same UC that I am in right now, our department (I don't know if our whole school has this, though) requires full-time pay as RA or TA for the summer. So, this adds about about $9000 for the 3 months of summer.
I'm only a first year, but I haven't really felt like I have to watch my money very carefully (well, mostly the studying, classes, responsibilities take precedence over a lot of other things I do). I send my parents about $300~$600 dollars of my stipend a month to pay them back slowly for paying for my undergrad. I eat out about once a week, but mostly eat what I "cook" (rice and whatever the hell I dump into the rice cooker usually..). I don't really buy much stuff in that sense. I do fly back home about once or twice a quarter (a round trip can cost from $100~$200). Overall, I don't think that the stipend offered by my UC is bad at all, especially since we have nice housing (somewhat recently constructed) for a lower cost than the surrounding area for a good twenty minute radius.
I don't know if UCs normally offer low stipends, but I think there is a kind of a set standard for stipends for the UC system due to our TA/RA unionization. However, in addition to those stipends, UCs will offer additional fellowships (like mine does, and I know that at least two other UCs do this too) for recruitment. So, if you have a much better offer from a comparable program (especially if your UC wants to rise in rankings), you probably could negotiate a recruitment fellowship addition to the stipend..
EDIT:
I forgot to mention that the numbers I put were before taxes. In addition, my housing situation is about $733/month (+$10~20 for electricity) for a two-story apartment with two bedrooms with two people total living in the apartment.