Well, here's the situation. I know UCSD is thought to be in La Jolla but it's not the same as downtown La Jolla. Downtown La Jolla is basically next to the beach and it's where all the rich/retired people live. Anything there will be super expensive.
The UCSD area actually has decent deals (still expensive compared to other places but cheaper than downtown La Jolla) if you want to get a 2-3 bedroom place and split the cost among roommates. The advantage is you're really close to school, the disadvantage is it's still somewhat expensive.
If you want to party, live cheaper, and live close to the beach, you can check out PB (Pacific Beach.) Tons of college kids, bars and clubs, and it's cheaper. The drive is about 15 minutes without traffic though.
There are places that are closer to UCSD (Clairemont Mesa, Mira Mesa) which are cheaper and somewhat close (10 minutes away without traffic.) Clairemont would probably be the cheapest but Mira Mesa is a little nicer.
The important thing to ask here though: are your roomates hot? You wanna introduce me to them? 😛