Flexible transport from LAX to Las Vegas?

My boyfriend and I will be taking a trip to the states in august. We will be spending 3 nights in Anaheim to do the Disneyland thing but sort of last minute decided we'd like to make a day trip to Las Vegas. So we are looking for some sort of transport, whether it be bus, train, etc, we arent fussed. Ideally we'd like to leave LA in the early morning to get to Vegas before mid day. And then we'd like to spend the day and leave late night from Vegas back to LA as we've already paid for all 3 nights accommodation in Anaheim. Can anyone recommend a service or services that they know of or have used? Thank you!