(Granted, not an herb or spice)
Fungi maybe? (
http://garden.org/ediblelandsc... ) however I have no idea what laws are in place for selling a fungus online. You might could sell to locals.
Cost would involve a basic setup , maybe a heating mat, container, soil (which can be used coffee grounds from that day) , and a dark room which you already have. Many many ideas off the internet on growing them.
