You just have to shop around for the best price. In 2014 I manage to get a return from Newcastle to Antwerp (Belgium) for £11.50.

When I go around the country I tend to drive, means I go at my own pace and have flexibility in my plans. Though when I do go to London I tend to use the coach, usually megabus, but would use NatEx if cheaper. As for roominess, I managed to bag the seat next to the emergency exit both ways meaning plenty of leg room.