Check quilt shows - ours has a "country store" where members donate used items. Many times you can get rulers for cheap. Also, having volunteered at the local Salvation Army store, there are lots of donated quilting items when someone is getting out of quilting. You might also check other charity shops. Oh, and if you google salvation army, there used to be a store (or maybe more than one) that sold online. Also, check with your friends - do they have rulers that they no longer want. Maybe they would sell to you for reasonable price.