As you don’t have a server which meets our installation requirements you might look at Omeka.net for hosting the occasional web exhibit. The url would be slightly different from your main website, but you could easily create cross-links in the menu (at least, from Omeka.net).
If your collections management system exports to CSV, you could use that. Or you could add your items as needed, which other historical societies have done.
You might look specifically at Site Examples and Tips and the Feature List