Cheapest way to travel the west coast of Australia, Perth to Darwin?

Should I take the Greyhound or rent a vehicle? We want to stop a lot and explore.Theres 2 of us traveling.

renting a car will be easier as you guys can stop wherever you want. But do make sure to get a more economic car to save some money on the fuel.

Either rent a car or try to pick up a cheap reliable one you can sleep in ( 4wd if possible) and you can always sell it after the hire company's don't like you taking their cars on dirt tracks and here is few in WA.
Then buy yourself a book of free camping areas you will be surprised on how many there is and then plan your trip so you don't waste petrol going to places that aren't worth it.
There is some expensive places to shop so try to shop were the locals do.
Been up and down the WA coast a few times and it is a long time between drinks so be prepared but it is worth the look.
My favorite Places Kalbarri,Monkey Mia,Exmouth and Coral Bay I didn't mind Broome but preferred a little place called Point Samson and on the way you pass Cossack well worth a look.I am jealous now so I hope you have a great time and take lots insect repellent and sunscreen.

With two of you, hitchhike. I have done it myself and there are plenty of people who do. It is a safe method of travel provided you use common sense. Renting a car will cost you a lot of extra money if you don't plan on driving it back to Perth. You have to pay for its return from Darwin.

Plan the trip very carefully. It is a long distance between towns, No water, very hot in the summer (Dec, Jan) and very wet in the north during the raining season. Some roads will be closed.

Fitzroy Crossing to Halls Creek road gets flooded during the wet.