>Has anyone used this method
Yes. Many times.
> or is there another way to lure swarms?
You can put all your "retired" queens in a jar of alcohol. The alcohol from the jar works pretty well. You can spend a lot more money than the lemongrass oil to buy lemongrass oil in little plastic vials from the bee supply places. They work fine too.
> If I buy a swarm trap they want $49.99 just to ship it . What is the method of useing the lemongrass oil?
How much to buy it? I would just use an old box. Any old box will do, but one that had bees in it will work better. An old ten frame deep is the PERFECT size and a five frame deep works ok. Old comb is a good lure as well.
Here's some reading for you:http://www.bushfarms.com/beesferal.htm