This could be the longest (in one direction) and cheapest ride on public buses ever taken. I've done it a dozen times to get to LAX from UCSD.

Total price: $5.15 (if starting @ UCSD in La Jolla)
Travel time: ~6 hours
Distance: ~100 miles of public bus travel

By far the cheapest way to get from La Jolla to LA (besides hitching of course)

First, here are the bus operators used (all fare info, route maps & schedules are available at their websites - thank you Internet!):

NCTD - North Couny Transit Department (http://www.gonctd.com)
OCTA - Orange County Transit Authority (http://www.octa.net)
LBT - Long Beach Transit (http://www.lbtransit.org)
MTA - Metro Transit Authority (http://www.mta.net)

Now, here's the fare breakdown:

$3.75 day pass on NCTD (w/free transfer to OCTA *upon request*)
$0.90 for LBT
$0.50 transfer from LBT to MTA bus/rail (valid for one ride only)
TOTAL: $5.15

Finally, here's the route starting at UCSD, ending up at LAX:

NCTD #101 to Oceanside Transit Ctr (ride to end)
NCTD #394 to San Clemente (ride to end)
OCTA #1 to Long Beach (get off at Westminster, walk towards bridge)
LBT A or D to LB transit center (ask for Transit Ctr)
MTA #232 to LAX (ride to end)

The OCTA #1 could be the cheapest cost per mile public bus ride in America. $1.50 for about 45 miles. And you always get a few interesting SoCal hobos joining you for the ride

This is for those who enjoy the ride just as much as the destination. Enjoy!