You do not need to buy these in advance, most parks with have a ticket booth at the entry point, otherwise an honesty box will be provided. Don’t assume that card or EFTPOS facilities will be available and carry enough cash. There will usually be a National Park office in the nearby town. If you purchase a day ticket and then decided to upgrade to one of the other passes (below), retain that ticket and get the price of the your day ticket refunded if you present that ticket to any National Park ticket agency within 7 days of purchase.
Single Entry (per a day) : $10 per a vehicle including up to to 8 passengers alternatively $5 per a person arriving on motorbike or $4 per a passenger in a bus
$20 per a vehicle for one, or a number of close-by parks, for 12 months e.g. Cape le Grand, Cape Arid and Stokes Inlet count as one local pass. So if you expect to spend more than 1 day in a particular park you might as well buy the annual local pass.
$35 per a vehicle for unlimited access to all WA parks for 4 weeks. You would have to be covering a lot of ground to make good use of this one, WA is a huge state.
$75 per a vehicle for unlimited access to all WA parks for 12 months.
These prices do not include camping fees, which are usually $5 to $7.50 per person depending on facilities. Camp fires are often not permitted so campers will need fuel or gas stove and to be self-sufficient in water.
For further information check the WA official site