I don't see why people bitch about Greyhound (pun semi-intended). It costs half as much as an Amtrak train through the northeastern United States, which is Amtrak's bread and butter route. Outside of that area, it's many times more cheaper. Every bus I've been on (quite a few) has been decently clean, and you get used to the smell of the toilets quickly. If you've got time to spare but not money, I recommend Greyhound as a means of travel.