Comment by lapcat

The OP was talking about monetary wealth. Here you're redefining "expensive" to mean something other than wealth, i.e., time.

Also, the whole point of the submitted article is that the investment of time into exercise is totally worth it.

Yes, there's a learning curve to tennis, as with any sport. You could just go jogging/running by yourself, but the advantage of sports, including tennis, is that they're usually a more fun and less boring form of exercise than jogging/running by yourself. If exercise is fun, then you're more likely to stick to it rather than skipping it.