I used to think it was based on how much each could afford or wanted to buy in paid ad time on the media. But according to The Broadcasting Arbitrator (yes, there is such a person), the amount of time any political party can purchase on the media seems to depend on how successful they are. 

On Wednesday, the office released the amount each one can buy. I don't think, no matter how much time they've been given, you're going to see a lot of paid pitches on TV or radio from the Rhinocerous Party or the Marxist-Lennist Party (14 minutes, 30 secs.) or even the Reforge Party (whatever that is), who get the same 14:30. 

In comparison, the more well known and successful political groups can get a lot more for their dollars depending on number of seats. Check out the list below.