It's not just the money, although that is a huge part of it. In places like Russia, Finland, and China (I pick these places because I know dancers from these places), people look on dancing as a fun exercise activity that is good for kids, and kids start it quite young -- just like kids in the US play soccer or little league. A Finnish woman I know told me there were about 1000 kids who would come to the sports school near her each week for lessons. In the US, there's only about 6000 registered amateur competitors, while in this one town in Finland outside of Helskini, there were about 1000 kids alone! The programs are geared toward teaching people in inexpensive group class situations, so that keeps the price lower. In China, people view dancing as a healthful activity that should be done every day as part of one's regular life -- some people do tai chi, some do gong fu, some dance ballroom.
Ballroom dancing in the US was long looked at as being something for old people, and because of the way the US studio system evolved it catered to wealthy older people, particularly women with lots of time and money on their hands. This is changing, thank goodness.
Another problem that people face in the US that they don't in places where ballroom dancing is more popular is the misplaced idea that boys who dance are gay. That is so completely ridiculous, yet it persists in the US, and makes it more difficult for boys and men to get involved. Hopefully the popularity of "Dancing with the Stars" in the US is changing this conception on a mass scale, too.