How to promote art directory to / for artists and online galleries ?

We run a free resource directory for artists and want to invite artists and galleries to add their listings. The service is totally free of costs, no mailing lists, nothing nasty. It’s at http://www.artistsinoils.com

Problem is no budget. How best to invite artists and art galleries, art museums, art teachers to take advantage of this service ?

You might find some helpful information here http://www.art-gallery.us