Welcome Lou & Em!
We had both our boys through Melbourne IVF, if you are looking at a clinic insem, it's probably a good idea to get the ball rolling now, as the waiting list for anonymous donor sperm is quite long. If you have a known donor you would like to use, there is still a wait of around 6 months for the sperm to pass quarantine.
The best place to start is a referral from your GP for a fertility specialist, they can answer all your questions including costs etc. John McBain at Melbourne IVF has helped loads of lesbian couples, he is probably a good person to get a referral for so he can give you more information.
Good luck !!