I've tested the dollar sign with the include_content_item plugin on both Joomla 1.0.15 and Joomla 1.5.10. Both seems to work fine.
You can see the actual test here.
I think you must have some plugins that strips away the dollar sign.
Would suggest you install a clean copy of Joomla somewhere on your system first - just to make sure that the dollar sign does work with the include_content_item plugin. Then you can slowly add other plugins to see which is the one that strips away the dollar sign.