El Sereno has become rougher in the past couple of years. Some is still fine, but even at the north end where it's cut off from South Pasadena, they have had some problems. The areas with apartment buildings tend to have more problems than the areas with houses. The closest community college to Montebello is East LA, it's a good community college, good transfer rate to UCLA.
You might want to take a look at Glendale and Pasadena. See if you can find a studio for around $800 in a nice neighborhood. (Most of both cities is nice, but there are some rough neighborhoods, but they will be obvious.) It may be tough to find anything cheaper. You might be able to find something in Alhambra the same or even a bit less. Alhambra is in between PCC and ELAC, about 5 miles from each. You will likely have the easiest time finding an apartment really close to PCC. Pasadena has decent public transportation in most areas, including the Gold Line and their local ARTS buses. GCC is up in the hills, so lots of houses, but also some apartments, and there is a bus line that goes there.
Drive around neighborhoods and look for smaller apartment buildings with rental signs posted in the front. Those will usually be buildings with less amenities, which often means less expensive. You can also go on campus and look at the boards for rental ads.
What about a job? If you need to work, wherever you find a job should be where you decide to live and go to school.
Glendale Community College and Pasadena City College are both very good community colleges.
GCC http://www.glendale.edu/
PCC http://www.pasadena.edu/
ELAC http://www.elac.edu/
Apartments:
PadMapper http://www.padmapper.com/
HotPads http://hotpads.com/
Neighborhood info:
http://www.lalife.com/ Click on Safety, then Map.
Good luck!