If I remember this subject has been brought up in the past and was always knocked down by members, especially those who are in the Bonsai Business.
Years ago there was a forum called the Gardenweb (I don't know if it is still around). They had a section for classifieds. I still remember someone wanted to trade Cactus for Bonsai seedlings. I sent the woman about 12 Cacti and received about 25 Bonsai seedlings in exchange. After that there was no stopping me, and I started leaning toward tropical trees, and have never turned back.