If the relay clicks, it isn't a busted switch
If I were you, I would take a length of wire, and test the horns...pop the relay out, have someone (gf?) hold the horn button, and try jumping the three prongs of the relay socket in different combinations to see if you can get the horn to go off. If you can, go down to Pep Boys and spend $1.50 on a relay. If you can't, go down to pep boys and spend $10 on a replacement horn...but I'd almost guaruntee it is the relay.