New Mexican budget airline VivaAerobus ( lives up to its name. Sometimes it's an airplane. Sometimes it's a bus. It's all in the service of the lowest fares possible.

"There are eight flights a day between Monterrey, Mexico and Houston, and they average $650," said VivaAerobus commercial director Juan Carlos Zuazua Cosio. In an online search, we found them for $469, but his point still holds. Viva does the route starting at $192.65 round trip, but you're on a bus part of the time.

VivaAerobus takes its ideas from its investors, a big Mexican bus company and the founders of the super-low-fare Ryanair airline in Europe. From Ryanair they get their ultra-low-cost, ultra-no-frills attitude. From Omnibus Mexicanos they get the buses.

Viva runs seven planes serving 18 Mexican cities and Austin, Texas out of their hub in Monterrey, Mexico. They serve Monterrey, CancĂșn and Puerto Vallarta direct from Austin for fares as little as $9.99 each way. They operate out of their own terminal in Austin, miles from the main terminal.

But you can also buy a ticket from Houston, San Antonio, El Paso, McAllen, Laredo, or San Diego to 27 Mexican cities on VivaAerobus. You just won't be on a plane the whole way. Sometimes, you'll be on a bus.

The VivaBus shuttle picks up passengers from depots in Houston and San Antonio and drops them at the front of the Viva terminal in Austin for $20, with bus times connecting with flight times. A similar shuttle drives El Paso residents across the border to hop on planes in Ciudad Juarez. Buses from Laredo and McAllen go all the way to Monterrey before turning into planes. By January, San Diego residents will get a quick bus shuttle to Tijuana, according to Zuazua.

The quality of the buses varies. In the US, they're mostly just vans; this is, after all, a low-fare airline. In Mexico, they're more likely to be the big, relatively plush buses that were the mainstay of Mexican intercity transportation until that country's low-fare airline sector started expanding a few years ago.

The buses pull up to the front of Viva's terminals with a little less than two hours for passengers to check in and make their flights. It's not a quick connection, just a cheap one. The bus drivers are in touch with the terminal by radio, but the only time they've missed their connection was because of a hurricane, Zuazua said.

On the other end, buses pick up fliers in front of airport terminals to take passengers either directly to Mexican destinations like Ixtapa, or to a downtown bus terminal where they then connect to another bus to their destination. Viva discounts bus fares by 75% if you buy them with a plane ticket.

Viva's buses also close the gaps between airports and cities, with buses connecting to planes to take passengers downtown in 9 Mexican cities.

"In many US cities, you have a lot of forms of transportation when you arrive to the airport. In Mexico there's only taxis, and in some cases they're really expensive," Zuazua said.

Viva is an extreme low-fare airline. That means no reserved seats, no free food or drink, no U.S.-based phone number, and most importantly, no guaranteed air-to-air connections. While you can book tickets through Monterrey, if you miss your connection for any reason -- even if it's Viva's fault -- you're just out of a ticket.

Viva advertises their bus connections online, but the routes weren't bookable when we checked on Nov. 14-17. Zuazua said this was because of a technical error that would be fixed within a week.

Viva has also come under criticism from some passengers for changing flight schedules by days at a time. Zuazua said this only happened once so far, because of a switch between high-season and low-season schedules, and that they will always try to notify passengers via e-mail or phone if schedules change. But still, we'd recommend not buying Viva tickets months in advance in case the airline changes their routes or schedules.

Viva isn't the first airline to combine air and land transport on the same ticket. Since 2002, Continental Airlines has "served" several Northeastern cities including Philadelphia and New Haven through a code-share with Amtrak. Amtrak trains appear on Continental tickets as a "flight operated by Amtrak." And air/rail code-shares in Europe are pretty common.

So yeah -- it's basic. Very, very basic. But when you're talking $20 for a flight to Mexico, well, just think about this: It's quicker than taking the bus the whole way.