I paid $53 for a PIAA Automotive Superior Bass Horn (330/400Hz)
It contains two speakers, took a little hunting to find a mounting for the second horn, but it works well. I went with it because I didn't need install a secondary relay and the DB output was satisfactory to me. Sounds more like a Mercedes horn now.
Trivia: I just got back from a European tour and learned that in some countries smaller cars must have higher pitch horns, while larger vehicles must have lower pitch horns.