I get asked daily on tips on how to buy and sell gold, and when it comes down to it, the margins on gold get worse and worse and more and more people try to start up shops. The known/large traders of today are simply too far ahead of anyone wishing to start up now.
However, there are plenty of ways to make money on runescape, and in no way should you disregard runescape as a possible source of income while it still exists. I made around $1000 in a month (I believe may-june of last year) of pking in high risk, for example.