Considering the least amount of dust you can receive is 3. Making you a 21g profit after, but we'll round that down to 20g.
The earth say you buy them from trade for 7-8 gold a pop, we'll say 8. Costs 2 to make one ring. So you buy 2. 2 = 16g
20g - 16g = 4g profit
Note that is the LOWEST POSSIBLE PROFIT you can get.
Now if you get a 5 stack, 4 stack, or a greater you'll be making even more money.
So yes, its worth it.