Race69 is right it's cheque book racing, those with the money will run the series.
I ran some numbers to run the whole series, if my son and I flew to all rounds except Shepparton where we coud drive, I'm looking at $4k in flights. Throw in around another $3-4K for accomodation remembering you need to be at the Nationals for a week. My accomodation figures are based on approx $150 a night, around $600 per event, and $1K for the Nationals. Add in car hire for the fly away rounds, entries and food, I can't see much change from $10K.
As for the timing of the Nationals, NOT the National SERIES, I can see that BMXA are trying to minimise costs for riders. In that I mean that if an event is held outside school holidays, the cost of flights and accomodation are reduced. Have a look at flights in and outside peak dates and you'll see what I mean. Accomodation is the same.