LaGuardia to Newark and vice versa
 

Can anyone recommend an efficient way to get between LGA and EWR? Any idea how much a cab would cost?

Thanks, good info.

There's no efficient way, but a cab is the fastest. Expect to pay about $100 or so if you use this option.

The airport bus option isn't a bad one. If you go that route, I'd actually recommend taking NY Airport Service to Grand Central and then switching to Olympia Trails, which is about 2 blocks away.

Another decent alternative is NY Airport to Penn Station and then NJ Transit to Airtrain to EWR. The price will be similar to the 2-bus option but a little trickier for the transfer.

Just remeber that there are a significant number of time-delay risks to this transfer. You have to get from Queens across or under the river to Manhattan, across Manhattan, across the Hudson to New Jersey, and then to Newark. Each leg is subject to traffic delays from rush hours, accidents, and weather. Each crossing requires a choke point delay also. Choice of cab or bus is irrelevant under adverse traffic conditions.