It varies a bit depending on where you are so do some googling but in Vic I think roughly you can expect to pay:

Trainee - free or just cover costs (parking and petrol)
Newly qualified - $800ish
Experienced - $1000-$1500ish depending on experience.

Bear in mind that a doula will be on call for you 24/7 from a couple of weeks before your due date until your baby is born...so that can be up to 4 weeks if you go past your date.

Fees usually include a set number of visits in your home, access to resource library, attendance at birth and one or two postnatal visits.

Good luck