there's loads of work out there in the Real Estate market. Just don't underprice yourself, stick to your guns, and let everyone know who you are and what you do, it's a numbers game, don't expect to shoot every house an agent has, but if they get a good one they'll push for good photography as they know the impact it has on their marketing. Your locale makes a difference as well, it's not much use marketing yourself in the boondocks, but if you're in the Hills go for it!
$40.00 a house wouldn't be worth getting out of bed for. But if you diferentiated yourself from that, as in created stunning images beyond what is expected, then you'll be able to charge for them.
A major part of it is being very accomodating and being able to do it within a day or 2 max, if you are unable to do this then don't even bother wasting your time marketing as they really want a fast turn around.
Also bear in mind that they have to trust you explicitly, as they are sending you to their clients house. The better they know you the better off you'll be, I wouldn't expect any jobs until you've done a few rounds of the agencies and they've got to know you.