3-4+ hours should be enough. United and US air have flights to LAS. It's quite expensive because it's so last minute -$161 oneway per/person. Normally, if u buy it early enough it's only ~$60. Southwest also has flights almost every hour $10 more expensive ~170..but bags are free to check in. United and US you'll have to pay ~15-20 p/bag.

If you're flexible on time and willing to change airports, Jetblue has a flight at 8PM out of Long Beach Airport(LGB) and it's only 114 per person. Not sure how willing you are to do that.. esp with 5people.