Southwest has announced its first routes out of its new base in New York's LaGuardia airport and--tah dah!--no surprise here,they're to Baltimore and Chicago. Fares will be set initially at $49 each way to BWI and $89 to Chicago Midway. Not quite as cheap at the Bolt Bus, but remember that Southwest lets you change your reservation without a penalty (they'll give you a credit good for future travel, which you can apply to any fare). The other airlines, although they charge as little as $78 RT between New York and Washington's two other airports (DCA and IAD) charge up to $150 to make a change.
From Baltimore and Chicago, you can fly almost anywhere on the Southwest system. For example, LGA to Vegas is $99 each way at present.