If your starting point is in Sydney and then Virgin Blue has direct flights from Sydney daily week. Ticket prices vary, but Virgin Blue is very reliable, their daily flights in the morning and arrive in Hervey Bay. Time to control virgin site because of the departure of the year will depend, of Sydney, and arrival time Hervey Bay.
If your starting point is Melbourne, then you need to go to Sydney to get the first flight or connecting Brisbane with Qantas link, but check the price, because you may find that in order to avoid Qantas Link, will save you money.
If your starting point is Brisbane Qantas link then, including every day of the week, more than one flight a day.