PT worked for me, but it gets really expensive, too.

Though maybe a few visits to learn some exercises would help? When I was doing PT, I did a number of stretches - things you could do easily at home include sitting with "good" leg/foot down (as in a chair), and the "bad" side with your foot over the good. Almost crossing your legs but with your lower leg resting on the upper one. Then lean over as far as you can, and you should feel a good stretch in the SI joint/ligaments.
Another thing that I found helpful was to focus on posture while walking. In PT, I did this as an exercise in the water, but found relief on dry land, too. I think it was as simple as pulling in abs, tucking under bum, and pulling shoulders back a bit. Walk like that, and it may help.
Also, my chiro has done massage on my SI joint area that has helped a lot. I can't really describe it, but there are a few different muscles in the area that can get really tight - one going down the side of the leg, another in the glute. A good massage therapist might help, or working on it on your own or having your DH do it. (My DH is more effective at reaching the glute!)
I couldn't survive without my chiro, though. I have found a really super good one, and I'm very glad our insurance covers her!