The cheapest way to get from LAS to OAK is probably on Aloha. Although their flight times aren't ideal (departure 5:45am), it can be had for $160 RT.
Orbitz gave me some LAS-LAX-SFO options on TED and UA for around the same prices as the nonstops but ual.com wouldn't price it the same way. There were also some connections through SMF.
Check Orbitz.
I recently paid $204 for an upcoming weekend SFO-LAS trip. Days of the week make a big difference in this market.