My insurance doesn't cover them, and at my OB's office they are $200. But they have had the 3D/4D machines in there for a while now. Your OB possibly has one.
Many Ob's have them in their office. Just ask your doctor at your next visit. Or you could look in the yellow pages =) I found lots of ads for them in there when I was thinking about getting one.
This is where I found mine. They will email you the closest.
I also did a search and still hadn't found one closer then the one they sent me. I get it done this tuesday $189.00