As a beginner, I really prefer the 30 minute race. The price difference doesn't bother me as during that extra 15 minutes of racing I'm most likely hanging out with other people or partaking in the food they provide, which is the real cost of these events.

For the races hosted by Tailwind, everyone pays the same fee except for the Elite men and women category (they pay $5 more).

Here's the flier for the next race (look at the second page):
http://tailwind-racing.com/Events/20...2011-10-01.pdf

As you can see, Cat-4 racers have the option of doing the 30minute or full 45 minute race. Everyone else does a full 45 minute race and I think that's a very nice way to organize.